connect: do not set QuerySource.Node

Setting this field to a value is equivalent to using the 'near' query paramter.
The intent is to sort the results by proximity to the node requesting
them. However with connect we send the results to envoy, which doesn't
care about the order, so setting this field is increasing the work
performed for no gain.

It is necessary to unset this field now because we would like connect
to use streaming, but streaming does not support sorting by proximity.

agent/agent.go

@@ -540,7 +540,6 @@ func (a *Agent) Start(ctx context.Context) error {
 		Logger: a.logger.Named(logging.ProxyConfig),
 		State:  a.State,
 		Source: &structs.QuerySource{
-			Node:       a.config.NodeName,
 			Datacenter: a.config.Datacenter,
 			Segment:    a.config.SegmentName,
 		},

agent/proxycfg/manager_test.go

@@ -352,10 +352,7 @@ func testManager_BasicLifecycle(
 	require := require.New(t)
 	logger := testutil.Logger(t)
 	state := local.NewState(local.Config{}, logger, &token.Store{})
-	source := &structs.QuerySource{
-		Node:       "node1",
-		Datacenter: "dc1",
-	}
+	source := &structs.QuerySource{Datacenter: "dc1"}
 
 	// Stub state syncing
 	state.TriggerSyncChanges = func() {}