Fix sporadic assertion failure in SocketSslEchoTest

Motivation:

SocketSslEchoTest.testSslEcho() has a race condition where a renegotiation future can be done before:

    assertThat(renegoFuture.isDone(), is(false));

Modifications:

Remove the offending assertion.

Result:

More build stability

testsuite/src/main/java/io/netty/testsuite/transport/socket/SocketSslEchoTest.java

@@ -276,7 +276,6 @@ public class SocketSslEchoTest extends AbstractSocketTest {
                 renegoFuture = clientSslHandler.renegotiate();
                 logStats("CLIENT RENEGOTIATES");
                 assertThat(renegoFuture, is(not(sameInstance(clientHandshakeFuture))));
-                assertThat(renegoFuture.isDone(), is(false));
             }
         }