HTTP/2 unit test failure race condition

Motivation:
HttpToHttp2ConnectionHandler is awaiting on a future and a latch that may be competed before the buffers actually get released.  This test is attempting to validate that the buffer's refCnt() is 0 but there is no mechanism to wait on for a buffer's release() method to be called.

Modifications:
Remove the buffer refCnt() check.  The leak profile is designed to pick these up.

Result:
Unit tests that no longer have a race condition.