bpo-42392: Improve removal of *loop* parameter in asyncio primitives (GH-23499)

* Update code after merge review from 1st1

* Use a sentinel approach for loop parameter
Remove unnecessary _get_running_loop patching

* Use more clear function name (_verify_parameter_is_marker -> _verify_no_loop)

* Add init method to _LoopBoundMixin to check that loop param wasn't used