Update change_form.html

Removed adminmedia load as indicated on:

https://docs.djangoproject.com/en/1.5/releases/1.5/#miscellaneous

The template tags library adminmedia, which only contained the deprecated template tag {% admin_media_prefix %}, was removed. Attempting to load it with {% load adminmedia %} will fail. If your templates still contain that line you must remove it.
Merge pull request #81 from AntonioReyes/patch-1

Removed adminmedia load