Remove the setuptools-provided distutils hack, if using distutils

This ensures that pip's imported copy of distutils comes from the
standard library, if/when the hack needs to be used.

src/pip/_internal/locations/_distutils.py

@@ -3,6 +3,14 @@
 # The following comment should be removed at some point in the future.
 # mypy: strict-optional=False
 
+# If pip's going to use distutils, it should not be using the copy that setuptools
+# might have injected into the environment. The least-worst option for ensuring this
+# seems to be to try to remove the injected shim, if it's injected.
+try:
+    __import__("_distutils_hack").remove_shim()
+except ImportError:
+    pass
+
 import logging
 import os
 import sys