Remove deprecated and outdated files.
Review Request #12004 — Created Jan. 26, 2022 and submitted
This change removes a bunch of things which are deprecated or no longer
- The datagrid and integrations apps had old templatetags files that
just raised warnings about their deprecation.
- We had a number of backports of newer django functionality to allow us
to maintain compatibility with Django 1.6.
- We had some stuff that provided compatibility with the importlib
module for Python versions that we no longer support (3.4 and below).
- The old
basictagdecorator has been deprecated for a long time.
Ran unit tests.