Asyncio watcher 'MultiLoopChildWatcher' currently doesn't work well
on Solaris and can freeze the event loop indefinitely.

This was reported upstream:
https://bugs.python.org/issue37573

--- Python-3.9.0/Lib/asyncio/unix_events.py
+++ Python-3.9.0/Lib/asyncio/unix_events.py
@@ -30,7 +30,7 @@ __all__ = (
     'SelectorEventLoop',
     'AbstractChildWatcher', 'SafeChildWatcher',
     'FastChildWatcher', 'PidfdChildWatcher',
-    'MultiLoopChildWatcher', 'ThreadedChildWatcher',
+    'ThreadedChildWatcher',
     'DefaultEventLoopPolicy',
 )
 
--- cpython-master/Lib/test/test_asyncio/test_subprocess.py
+++ cpython-master/Lib/test/test_asyncio/test_subprocess.py
@@ -684,11 +684,6 @@ if sys.platform != 'win32':
 
         Watcher = unix_events.ThreadedChildWatcher
 
-    class SubprocessMultiLoopWatcherTests(SubprocessWatcherMixin,
-                                          test_utils.TestCase):
-
-        Watcher = unix_events.MultiLoopChildWatcher
-
     class SubprocessSafeWatcherTests(SubprocessWatcherMixin,
                                      test_utils.TestCase):