Remove a racy and failing test

This test is super racy (it's not just a single line).

This test also starts failing once streaming is enabled, because the
cache rate limit no longer applies to the requests in the test. The
queries use streaming instead of the cache.

This test is no longer valid, and the functionality is already well
tested by TestCacheThrottle.  Instead of spending time rewriting this
test, let's remove it.

```
WARNING: DATA RACE
Read at 0x00c01de410fc by goroutine 735:
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:1024 +0x9af
  github.com/hashicorp/consul/testrpc.WaitForTestAgent()
      /home/daniel/pers/code/consul/testrpc/wait.go:99 +0x209
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:966 +0x1ad
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1193 +0x202

Previous write at 0x00c01de410fc by goroutine 605:
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1.2()
      /home/daniel/pers/code/consul/agent/agent_test.go:998 +0xe9

Goroutine 735 (running) created at:
  testing.(*T).Run()
      /usr/lib/go/src/testing/testing.go:1238 +0x5d7
  github.com/hashicorp/consul/agent.TestCacheRateLimit()
      /home/daniel/pers/code/consul/agent/agent_test.go:961 +0x375
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1193 +0x202

Goroutine 605 (finished) created at:
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:1022 +0x91e
  github.com/hashicorp/consul/testrpc.WaitForTestAgent()
      /home/daniel/pers/code/consul/testrpc/wait.go:99 +0x209
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:966 +0x1ad
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1193 +0x202
```

agent/agent_test.go

@@ -18,7 +18,6 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
-	"sync"
 	"testing"
 	"time"
 
@@ -30,7 +29,6 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sync/errgroup"
-	"golang.org/x/time/rate"
 	"google.golang.org/grpc"
 	"gopkg.in/square/go-jose.v2/jwt"
 
@@ -937,110 +935,6 @@ func testAgent_AddServiceNoRemoteExec(t *testing.T, extraHCL string) {
 	}
 }
 
-func TestCacheRateLimit(t *testing.T) {
-	if testing.Short() {
-		t.Skip("too slow for testing.Short")
-	}
-
-	t.Parallel()
-	tests := []struct {
-		// count := number of updates performed (1 every 10ms)
-		count int
-		// rateLimit rate limiting of cache
-		rateLimit float64
-		// Minimum number of updates to see from a cache perspective
-		// We add a value with tolerance to work even on a loaded CI
-		minUpdates int
-	}{
-		// 250 => we have a test running for at least 2.5s
-		{250, 0.5, 1},
-		{250, 1, 1},
-		{300, 2, 2},
-	}
-	for _, currentTest := range tests {
-		t.Run(fmt.Sprintf("rate_limit_at_%v", currentTest.rateLimit), func(t *testing.T) {
-			tt := currentTest
-			t.Parallel()
-			a := NewTestAgent(t, "cache = { entry_fetch_rate = 1, entry_fetch_max_burst = 100 }")
-			defer a.Shutdown()
-			testrpc.WaitForTestAgent(t, a.RPC, "dc1")
-
-			cfg := a.config
-			require.Equal(t, rate.Limit(1), a.config.Cache.EntryFetchRate)
-			require.Equal(t, 100, a.config.Cache.EntryFetchMaxBurst)
-			cfg.Cache.EntryFetchRate = rate.Limit(tt.rateLimit)
-			cfg.Cache.EntryFetchMaxBurst = 1
-			a.reloadConfigInternal(cfg)
-			require.Equal(t, rate.Limit(tt.rateLimit), a.config.Cache.EntryFetchRate)
-			require.Equal(t, 1, a.config.Cache.EntryFetchMaxBurst)
-			var wg sync.WaitGroup
-			stillProcessing := true
-
-			injectService := func(i int) {
-				srv := &structs.NodeService{
-					Service: "redis",
-					ID:      "redis",
-					Port:    1024 + i,
-					Address: fmt.Sprintf("10.0.1.%d", i%255),
-				}
-
-				err := a.addServiceFromSource(srv, []*structs.CheckType{}, false, "", ConfigSourceRemote)
-				require.Nil(t, err)
-			}
-
-			runUpdates := func() {
-				wg.Add(tt.count)
-				for i := 0; i < tt.count; i++ {
-					time.Sleep(10 * time.Millisecond)
-					injectService(i)
-					wg.Done()
-				}
-				stillProcessing = false
-			}
-
-			getIndex := func(t *testing.T, oldIndex int) int {
-				req, err := http.NewRequest("GET", fmt.Sprintf("/v1/health/service/redis?cached&wait=5s&index=%d", oldIndex), nil)
-				require.NoError(t, err)
-
-				resp := httptest.NewRecorder()
-				a.srv.handler(false).ServeHTTP(resp, req)
-				// Key doesn't actually exist so we should get 404
-				if got, want := resp.Code, http.StatusOK; got != want {
-					t.Fatalf("bad response code got %d want %d", got, want)
-				}
-				index, err := strconv.Atoi(resp.Header().Get("X-Consul-Index"))
-				require.NoError(t, err)
-				return index
-			}
-
-			{
-				start := time.Now()
-				injectService(0)
-				// Get the first index
-				index := getIndex(t, 0)
-				require.Greater(t, index, 2)
-				go runUpdates()
-				numberOfUpdates := 0
-				for stillProcessing {
-					oldIndex := index
-					index = getIndex(t, oldIndex)
-					require.GreaterOrEqual(t, index, oldIndex, "index must be increasing only")
-					numberOfUpdates++
-				}
-				elapsed := time.Since(start)
-				qps := float64(time.Second) * float64(numberOfUpdates) / float64(elapsed)
-				summary := fmt.Sprintf("received %v updates in %v aka %f qps, target max was: %f qps", numberOfUpdates, elapsed, qps, tt.rateLimit)
-
-				// We must never go beyond the limit, we give 10% margin to avoid having values like 1.05 instead of 1 due to precision of clock
-				require.LessOrEqual(t, qps, 1.1*tt.rateLimit, fmt.Sprintf("it should never get more requests than ratelimit, had: %s", summary))
-				// We must have at least being notified a few times
-				require.GreaterOrEqual(t, numberOfUpdates, tt.minUpdates, fmt.Sprintf("It should have received a minimum of %d updates, had: %s", tt.minUpdates, summary))
-			}
-			wg.Wait()
-		})
-	}
-}
-
 func TestAddServiceIPv4TaggedDefault(t *testing.T) {
 	if testing.Short() {
 		t.Skip("too slow for testing.Short")