fix: Remove unused files; add more tests; fix some Make targets and lint

[timmc-edx]

Remove unused files from root of each cookiecutter. These were not actually
used as they were not inside the {{cookiecutter.repo_name}} dir that
would lead to them being included.

More information on removals:

• openedx.yaml removed from xblock cookiecutter root and
  Set appropriate tags in openedx.yaml #334 filed to cover
  actually adding that tag. (The rest of the file was either redundant
  with what's in python-template, or obsolete.)
• requirements.txt was not used in CI or baking
• Makefiles were not used. This is unfortunate because the IDA one actually
  had some useful tests in it. I've moved those to the ci.yml workflow for
  expediency but they should really be put into the unit tests at some
  point so that they can be run locally. A lot of the django-app Makefile
  seemed to have been written while the repo was still in development, and
  relied on packages that are not installed.

For the moved tests to pass, I had to make some fixes to the IDA template:

• Add missing docs target to Makefile, although it doesn't quite work yet;
  filed make docs is broken on django-ida cookiecutter #339 for fixing
  this later.
• Add some long-line lint suppression where needed

Other improvements:

• Remove unused BAKE_OPTIONS from root Makefile
• Use short version of BROWSER script in django-ida Makefile to
  match other Makefiles
• Fix root Makefile so that it actually uses pip-sync rather than just
  installing it
• Update JWT_PUBLIC_SIGNING_JWK_SET to be readable and copyable as JSON
  (as is likely to be done for edx-platform in the ongoing JWK work)
• Made fake_translations Makefile target actually do something.

Merge checklist:
Check off if complete or not applicable:

• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, deadlines, tickets

[rgraber]

One question

[timmc-edx]

make docs is now failing. But guess what: The only reason it wasn't failing previously is that I hadn't added docs to the .PHONY list, so it was just saying make: 'docs' is up to date. and not actually building the docs. -.- Looking into it.

[timmc-edx]

I think make docs is failing in the IDA output because the cookiecutter.requires_django variable isn't being respected. This means that the "Configure Django for autodoc usage" block isn't included, so importing urls.py fails.

[rgraber]

Questions and suggestions for changelog

[rgraber]

no docs build :(

[timmc-edx]

Removed :-(

[rgraber]

Might also add "removed unused files in django-ida, django-app, and xblock"

[timmc-edx]

Added something like this

[timmc-edx]

OK, got one last thing squared away. Ready for re-review.

[rgraber]

LGTM