chore: Remove 'lint' extra from setup.py

[matthewfeickert]

Description

• Remove the 'lint' extra. All linting should be done through pre-commit now and so there is no need to have a specific lint extra.
• Remove the flake8 and black components of the lint workflow, as these are redundant to pre-commit.ci.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Remove the 'lint' extra. All linting should be done through pre-commit now
and so there is no need to have a specific lint extra.
* Remove the flake8 and black components of the lint workflow, as these are
redundant to pre-commit.ci.

[codecov]

Codecov Report

Merging #1943 (81db3f2) into master (ad1dd86) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1943   +/-   ##
=======================================
  Coverage   98.26%   98.26%           
=======================================
  Files          69       69           
  Lines        4439     4439           
  Branches      748      748           
=======================================
  Hits         4362     4362           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	25.81% <ø> (ø)
doctest	61.02% <ø> (ø)
unittests-3.10	96.14% <ø> (ø)
unittests-3.7	96.13% <ø> (ø)
unittests-3.8	96.17% <ø> (ø)
unittests-3.9	96.19% <ø> (ø)

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