Remove admin files deprecated in Django 1.4

Remove "ADMIN_MEDIA_PREFIX" (deprecated in Django 1.4)

Delete lms/static/admin resources as they are no longer needed
for the admin page as of Django 1.4

Moved two files that were referenced elsewhere:
lms/static/admin/js/jquery.min.js -> lms/static/js/admin/jquery.min.js
lms/static/admin/js/urlify.js -> lms/static/js/admin/urlify.js


"ADMIN_MEDIA_PREFIX" and having css/js assets were necessary for the admin page in Django 1.3 but was deprecated in 1.4. We no longer need these files and the admin page works just fine without them. See https://docs.djangoproject.com/en/1.4/ref/settings/ for reference.
Shouldn't we just use the version of jQuery that lives at `common/static/js/vendor/jquery.min.js`, like we do everywhere else? Then we could get rid of this extra jQuery file, as well.