netty,okhttp: Enable TransportTest.flowControlPushBack

It appears to be stable now. Ran for 1000s of times. I do see some
general flakiness in TransportTest, but it applies to the tests in
general and isn't specific to this one test. It is:

```
org.mockito.exceptions.verification.WantedButNotInvoked:
Wanted but not invoked:
listener.transportReady();
-> at io.grpc.internal.testing.AbstractTransportTest.startTransport(AbstractTransportTest.java:1815)
Actually, there were zero interactions with this mock.
```

This flake is not seen often because it occurs less frequently when
running all the tests (~.1% vs 1%). One of the early tests must warm
something up to make it less likely.

1 files changed, 0 insertions, 7 deletions

diff --git a/netty/src/test/java/io/grpc/netty/NettyTransportTest.java b/netty/src/test/java/io/grpc/netty/NettyTransportTest.java
index cb5dee943..1aa4c12f2 100644
--- a/netty/src/test/java/io/grpc/netty/NettyTransportTest.java
+++ b/netty/src/test/java/io/grpc/netty/NettyTransportTest.java
@@ -26,8 +26,6 @@ import java.net.InetSocketAddress;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import org.junit.After;
-import org.junit.Ignore;
-import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
@@ -99,9 +97,4 @@ public class NettyTransportTest extends AbstractTransportTest {
         new ClientTransportFactory.ClientTransportOptions()
           .setAuthority(testAuthority(server)));
   }
-
-  @Test
-  @Ignore("flaky")
-  @Override
-  public void flowControlPushBack() {}
 }