Fixed #27781 -- Made simplify_regex() remove outstanding '?' characters.

Regression in f0ef0c49.

django/contrib/admindocs/views.py

@@ -430,7 +430,7 @@ def simplify_regex(pattern):
     pattern = replace_named_groups(pattern)
     pattern = replace_unnamed_groups(pattern)
     # clean up any outstanding regex-y characters.
-    pattern = pattern.replace('^', '').replace('$', '')
+    pattern = pattern.replace('^', '').replace('$', '').replace('?', '')
     if not pattern.startswith('/'):
         pattern = '/' + pattern
     return pattern

tests/admin_docs/test_views.py

@@ -336,6 +336,7 @@ class AdminDocViewFunctionsTests(SimpleTestCase):
             (r'^(?P<a>(x|y))/b/(?P<c>\w+)$', '/<a>/b/<c>'),
             (r'^(?P<a>(x|y))/b/(?P<c>\w+)ab', '/<a>/b/<c>ab'),
             (r'^(?P<a>(x|y)(\(|\)))/b/(?P<c>\w+)ab', '/<a>/b/<c>ab'),
+            (r'^a/?$', '/a/'),
         )
         for pattern, output in tests:
             self.assertEqual(simplify_regex(pattern), output)