[chore] remove TODO from confighttp tests (#9121)

Since the listener is already listening, the Serve call will not
introduce a delay in processing requests.
It is then fair to block the main thread on waiting the goroutine to be
started, and unblock before Serve is called.

Author: atoulme

config/confighttp/confighttp_test.go

@@ -706,9 +706,6 @@ func TestHttpReception(t *testing.T) {
 				_ = s.Serve(ln)
 			}()
 
-			// Wait for the servers to start
-			<-time.After(10 * time.Millisecond)
-
 			prefix := "https://"
 			expectedProto := "HTTP/2.0"
 			if tt.tlsClientCreds.Insecure {
@@ -821,10 +818,6 @@ func TestHttpCors(t *testing.T) {
 				_ = s.Serve(ln)
 			}()
 
-			// TODO: make starting server deterministic
-			// Wait for the servers to start
-			<-time.After(10 * time.Millisecond)
-
 			url := fmt.Sprintf("http://%s", ln.Addr().String())
 
 			expectedStatus := http.StatusNoContent
@@ -941,10 +934,6 @@ func TestHttpServerHeaders(t *testing.T) {
 				_ = s.Serve(ln)
 			}()
 
-			// TODO: make starting server deterministic
-			// Wait for the servers to start
-			<-time.After(10 * time.Millisecond)
-
 			url := fmt.Sprintf("http://%s", ln.Addr().String())
 
 			// Verify allowed domain gets responses that allow CORS.
@@ -1346,9 +1335,6 @@ func BenchmarkHttpRequest(b *testing.B) {
 		_ = s.Close()
 	}()
 
-	// Wait for the servers to start
-	<-time.After(10 * time.Millisecond)
-
 	for _, bb := range tests {
 		hcs := &HTTPClientSettings{
 			Endpoint:   "https://" + ln.Addr().String(),