Replace flake8 with autoflake

autoflake automatically fixes the code while flake8 just report it.

• Replace flake8 with autoflake pre-commit hook
• CI: run autoflake instead of flake8.

changed milestone to %0.11.0

added CI/CD Dev Env enhancement labels

assigned to @moul

mentioned in commit aefc7d7c

mentioned in merge request !222 (merged)

mentioned in commit cf0079df

closed with merge request !222 (merged)