test: fix test by removing non-member attribute

Author: felixscherz

Lib/test/test_typing.py

@@ -4557,7 +4557,6 @@ class Commentable(Protocol):
     def test_isinstance_with_deferred_evaluation_of_annotations(self):
         @runtime_checkable
         class P(Protocol):
-            x: int
             def meth(self):
                 ...