Update pylint to 2.7.3

[cdce8p]

Proposed change

Changelog: http://pylint.pycqa.org/en/latest/whatsnew/changelog.html#what-s-new-in-pylint-2-7-3
Full diff: pylint-dev/pylint@pylint-2.7.2...pylint-2.7.3

Note-worthy changes

• Custom name preset for class constants (which include Enums): Add --class-const-naming-style pylint-dev/pylint#4185
• Fix for false-positive unused-import: Fix false-positive for unused-import on class keyword arguments pylint-dev/pylint#4207
  It's no longer necessary to use pylint: disable=unused-import in **/config_flow.py. This removes a lot of disables.
• Fix for false-positive no-member for typed annotations without default value: Fix false-positive no-member for typed annotations without default value pylint-dev/pylint#4194
  @frenck If I remember correctly, you complained about this one quite a bit ;)

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

home-assistant/developers.home-assistant#871

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the [development checklist][dev-checklist]
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

[bdraco]

Those are some nice fixes 👍

[frenck]

Aah that cleans stuff up really nice there @cdce8p 👍