The `# -*- coding: utf-8 -*-` headers were useful for Python 2, and
aren't needed for Python 3 where UTF-8 is the default.
yamllint support of Python 2 was dropped in early 2021, see commit
a3fc64d "End support for Python 2".
Let's drop these headers.
Instead of iterating over lines and tokens (and find comments between
tokens in the comment rules), add a new `Comment` type and set rules
with `type = 'comment'`.
Adrien Vergé
Hugo