Remove most Django compat usage and code.
Review Request #11626 — Created May 26, 2021 and submitted
This gets rid of most of the
updates all call sites to use the versions available in Django 1.11+.
Mostly, this is template-related code or management command code.
There are some changes in behavior for template code, functionality
differences around contexts that the old compat code papered over and
now needs manual changes. Mostly this involves calling
context.flatten()when calling render functions.
Unit tests pass on Django 1.11.