unify pylintrc and always run black

[graingert]

In #2735 unsupported python versions were dropped, so only one pylint config is needed and black can always run.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • unify pylintrc
  • always run black
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[alexcjohnson]

💃 Much nicer, thanks! Rerunning the failed test now...