remove unused variable to fix lint

Author: chandra-siri

tests/asyncio/test_bidi_async.py

@@ -287,7 +287,7 @@ async def test_send_dead_rpc(self):
         bidi_rpc = bidi_async.AsyncBidiRpc(None)
         bidi_rpc.call = AsyncClosedCall(error)
 
-        with pytest.raises(ValueError) as exc_info:
+        with pytest.raises(ValueError):
             await bidi_rpc.send(mock.sentinel.request)
 
     @pytest.mark.asyncio