Revert "Fixed #22867 -- Memoized django.utils.version.get_git_changeset()."

This reverts commit 80f4487d temporarily, because that commit prevented
the djangoproject.com server from building the docs, because it still
uses Python 2.6.

django/utils/version.py

@@ -4,8 +4,6 @@ import datetime
 import os
 import subprocess
 
-from django.utils.lru_cache import lru_cache
-
 
 def get_version(version=None):
     "Returns a PEP 386-compliant version number from VERSION."
@@ -52,7 +50,6 @@ def get_complete_version(version=None):
     return version
 
 
-@lru_cache()
 def get_git_changeset():
     """Returns a numeric identifier of the latest git changeset.