Configure autoflake for pre-commit

[akx]

Proposed change

This PR configures the autoflake linter in the pre-commit configuration and runs it. (I checked with git log -S autoflake that this hadn't been considered before.)

The main benefit is that autoflake can clean up unused imports and variables that other linters down the line would complain about.

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)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Checklist

• The code change is tested and works locally.
• Local tests pass.
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[frenck]

Thanks @akx 👍

[balloob]

What’s the benefit of autoflake while we also use Black ?

[frenck]

It cleans up unused imports (that is basically all it does). Not much more (so it doesn't do the full flake8 suite, as the name implies).