gh-117657: Remove TSAN suppressions for _abc.c (#121508)

The functions look thread-safe and I haven't seen any warnings issued
when running the tests locally.

Author: colesbury

Tools/tsan/suppressions_free_threading.txt

@@ -23,8 +23,6 @@ race:free_threadstate
 
 # These warnings trigger directly in a CPython function.
 
-race_top:_add_to_weak_set
-race_top:_in_weak_set
 race_top:_PyEval_EvalFrameDefault
 race_top:assign_version_tag
 race_top:new_reference