Unreachable assertion in test_conf_async_trio_requests

[langston-barrett]

This assert follows a return, so it's trivially unreachable:

https://github.com/Azure/msrest-for-python/blob/8896f85c559786213e7f7f4438cce20ab60b820c/tests/asynctests/test_universal_http.py#L84-L85

[lmazuel]

Thanks! That's true, but not critical, so keeping this issue open for the next time I do a batch of changes in tests ;)