Remove adminmedia here too.
Remove __metaclass__ hack.

We may need to restore this. We do this because __metaclass__ has been
removed in Django 1.5 as part of the port to Python 3. There is a way
to do this that's compatible in 2 & 3 but it's unclear if we need this
at all.
Remove attributes in admin.
Do not display Redirect in admin.
Remove `.defaults` (deprecated in newer Django versions).