test(transport): Remove background tasks from transport tests

GH-4601

Author: srothh

tests/test_transport.py

@@ -880,9 +880,7 @@ async def send_message(i):
 
     tasks = [send_message(i) for i in range(num_messages)]
     await asyncio.gather(*tasks)
-    transport = client.transport
     await client.close(timeout=2.0)
-    assert len(transport.background_tasks) == 0
     assert len(capturing_server.captured) == num_messages