manage.py attempted to load any extensions in order to factor in their

models for database upgrades and management commands for execution. This

hasn't actually been needed for a while, and isn't compatible with

Django 1.11 at all.
This change removes this logic entirely from manage.py.

Verified that management commands worked correctly on Django 1.6 and 1.11,

and that upgrades worked on Django 1.6 (and were attempted on 1.11, though

that requires more work to complete compatibility).