Deprecation and test cleanup (#1818)

* Remove remove_route, deprecated in 19.6.

* No need for py35 compat anymore.

* Rewrite asyncio.coroutines with async/await.

* Remove deprecated request.raw_args.

* response.text() takes str only: avoid deprecation warning in all but one test.

* Remove unused import.

* Revert unnecessary deprecation warning.

* Remove apparently unnecessary py38 compat.

* Avoid asyncio.Task.all_tasks deprecation warning.

* Avoid warning on a test that tests deprecated response.text(int).

* Add pytest-asyncio to tox deps.

* Run the coroutine returned by AsyncioServer.close.

Co-authored-by: L. Kärkkäinen <tronic@users.noreply.github.com>

tests/test_response.py

@@ -30,6 +30,7 @@ from sanic.testing import HOST, PORT
 JSON_DATA = {"ok": True}
 
 
+@pytest.mark.filterwarnings("ignore:Types other than str will be")
 def test_response_body_not_a_string(app):
     """Test when a response body sent from the application is not a string"""
     random_num = choice(range(1000))