Remove pkg_resources era safe_extra()

PEP 685 renders this normalization helper useless.

Author: ichard26

src/pip/_internal/utils/packaging.py

@@ -1,13 +1,10 @@
 import functools
 import logging
-import re
-from typing import NewType, Optional, Tuple, cast
+from typing import Optional, Tuple
 
 from pip._vendor.packaging import specifiers, version
 from pip._vendor.packaging.requirements import Requirement
 
-NormalizedExtra = NewType("NormalizedExtra", str)
-
 logger = logging.getLogger(__name__)
 
 
@@ -44,15 +41,3 @@ def get_requirement(req_string: str) -> Requirement:
     # minimize repeated parsing of the same string to construct equivalent
     # Requirement objects.
     return Requirement(req_string)
-
-
-def safe_extra(extra: str) -> NormalizedExtra:
-    """Convert an arbitrary string to a standard 'extra' name
-
-    Any runs of non-alphanumeric characters are replaced with a single '_',
-    and the result is always lowercased.
-
-    This function is duplicated from ``pkg_resources``. Note that this is not
-    the same to either ``canonicalize_name`` or ``_egg_link_name``.
-    """
-    return cast(NormalizedExtra, re.sub("[^A-Za-z0-9.-]+", "_", extra).lower())