bpo-43216: Remove @asyncio.coroutine (GH-26369)

Remove the @asyncio.coroutine decorator
enabling legacy generator-based coroutines to be compatible with async/await
code; remove asyncio.coroutines.CoroWrapper used for wrapping
legacy coroutine objects in the debug mode.

The decorator has been deprecated
since Python 3.8 and the removal was initially scheduled for Python 3.10.

Lib/test/test_asyncio/test_events.py

@@ -17,6 +17,7 @@ import subprocess
 import sys
 import threading
 import time
+import types
 import errno
 import unittest
 from unittest import mock
@@ -2163,8 +2164,7 @@ class HandleTests(test_utils.TestCase):
                         '<Handle cancelled>')
 
         # decorated function
-        with self.assertWarns(DeprecationWarning):
-            cb = asyncio.coroutine(noop)
+        cb = types.coroutine(noop)
         h = asyncio.Handle(cb, (), self.loop)
         self.assertEqual(repr(h),
                         '<Handle noop() at %s:%s>'