remove 3.15 warnings_helper

Author: gpshead

Lib/test/_test_multiprocessing.py

@@ -5849,7 +5849,6 @@ def test_context(self):
     def _dummy_func():
         pass
 
-    @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
     def test_spawn_dont_set_context(self):
         # Run a process with spawn or forkserver context may change
         # the global start method, see gh-109263.