Removed hacky url config (reverts #291)

I've hated this bit of code since I had to write it. It makes creating frontend login views more difficult than it should be so it's time for it to go.

wagtail/wagtailadmin/urls.py

@@ -96,13 +96,6 @@ urlpatterns += [
 ]
 
 
-# This is here to make sure that 'django.contrib.auth.views.login' is reversed correctly
-# It must be placed after 'wagtailadmin_login' to prevent this from being used
-urlpatterns += [
-    url(r'^login/$', 'django.contrib.auth.views.login'),
-]
-
-
 # Import additional urlpatterns from any apps that define a register_admin_urls hook
 for fn in hooks.get_hooks('register_admin_urls'):
     urls = fn()