Remove black while support is maintained for python 2.7

[ddrthall]

What does this PR do?

Remove the black tox command.
Force the mypy tox env to one that is supported.

Description of the Change

Python 2.7 support is being retired in a number of the utilities we're using to perform code verification. Black, a python formatter, is currently unsafe to run for python < 3.3 and therefore the ability to do so is being disabled while python 2.7 is still under support for this repo.
MyPy is currently version locked to support 2.7 static analysis, and fails to run successfully on python > 3.8. As such, it is defaulted to 3.8, the latest stable version that, at the time of writing, also boasts the most extensive pipeline support for the repo.

Alternate Designs

Possible Drawbacks

We want a formatter for the project, so disabling black is not the solution we ultimately wish to run with. While it might be possible to isolate a specific older version of black that 1) won't break support for 2.7 and 2) won't recommend unideal format changes for 3.12, such a solution would be brittle and increasingly unlikely to work as new python versions get released. We've already disabled the black run in the pipeline and don't seem to be running it locally, so a total removal was judged as more sensible while support for 2.7 remains.

Verification Process

None, no code changed.

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• PR should not have do-not-merge/ label attached.
• If Applicable, issue must have kind/ and severity/ labels attached at least.