e2e: test /metrics, /health endpoint in grpc-proxy

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

e2e/metrics_test.go

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build !cluster_proxy
-
 package e2e
 
 import (