Revert "Fix mypy failure that has nothing to do with this PR"

This reverts commit 4a3782d.

importlib_metadata/__init__.py

@@ -440,7 +440,7 @@ def at(path: str | os.PathLike[str]) -> Distribution:
         :param path: a string or path-like object
         :return: a concrete Distribution instance for the path
         """
-        return PathDistribution(cast(SimplePath, pathlib.Path(path)))
+        return PathDistribution(pathlib.Path(path))
 
     @staticmethod
     def _discover_resolvers():