bpo-42403: Use @staticmethod in importlib (GH-23395)

Use @staticmethod on methods using @classmethod but don't use their
cls parameter on the following classes:

* BuiltinImporter
* FrozenImporter
* WindowsRegistryFinder
* PathFinder

Leave methods using @_requires_builtin or @_requires_frozen unchanged,
since this decorator requires the wrapped method to have an extra parameter
(cls or self).

Lib/importlib/_bootstrap.py

@@ -761,16 +761,16 @@ class BuiltinImporter:
         spec = cls.find_spec(fullname, path)
         return spec.loader if spec is not None else None
 
-    @classmethod
-    def create_module(self, spec):
+    @staticmethod
+    def create_module(spec):
         """Create a built-in module"""
         if spec.name not in sys.builtin_module_names:
             raise ImportError('{!r} is not a built-in module'.format(spec.name),
                               name=spec.name)
         return _call_with_frames_removed(_imp.create_builtin, spec)
 
-    @classmethod
-    def exec_module(self, module):
+    @staticmethod
+    def exec_module(module):
         """Exec a built-in module"""
         _call_with_frames_removed(_imp.exec_builtin, module)
 
@@ -831,8 +831,8 @@ class FrozenImporter:
         """
         return cls if _imp.is_frozen(fullname) else None
 
-    @classmethod
-    def create_module(cls, spec):
+    @staticmethod
+    def create_module(spec):
         """Use default semantics for module creation."""
 
     @staticmethod