Replace flake8 with pylint

[zFernand0]

If we're adopting pylint then should we remove all references to flakes8 rather than having a mix of both?

• Remove step that runs flake8 in this workflow
• Remove pyflakes dependency from requirements.txt
• Update .vscode/settings.json to include setting that enables Pylint in VS Code
• Replace flakes8 with pylint in "Code Standards" section of CONTRIBUTING.md

Originally posted by @t1m0thyj in #317 (comment)

[github-actions]

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