Ensure that Proxies ARE always cleaned up, event with DeregisterCriticalServiceAfter (#4649)

This fixes https://github.com/hashicorp/consul/issues/4648

agent/agent.go

@@ -1818,6 +1818,15 @@ func (a *Agent) RemoveService(serviceID string, persist bool) error {
 		}
 	}
 
+	// Remove the associated managed proxy if it exists
+	for proxyID, p := range a.State.Proxies() {
+		if p.Proxy.TargetServiceID == serviceID {
+			if err := a.RemoveProxy(proxyID, true); err != nil {
+				return err
+			}
+		}
+	}
+
 	a.logger.Printf("[DEBUG] agent: removed service %q", serviceID)
 	return nil
 }

agent/agent_endpoint.go

@@ -682,15 +682,6 @@ func (s *HTTPServer) AgentDeregisterService(resp http.ResponseWriter, req *http.
 		return nil, err
 	}
 
-	// Remove the associated managed proxy if it exists
-	for proxyID, p := range s.agent.State.Proxies() {
-		if p.Proxy.TargetServiceID == serviceID {
-			if err := s.agent.RemoveProxy(proxyID, true); err != nil {
-				return nil, err
-			}
-		}
-	}
-
 	s.syncChanges()
 	return nil, nil
 }