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>

tox.ini

@@ -9,6 +9,7 @@ setenv =
 deps =
     coverage
     pytest==5.2.1
+    pytest-asyncio
     pytest-cov
     pytest-sanic
     pytest-sugar