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.
Using either 'yes', 'no' or 'whatever', the user will be able to choose
whether to force block sequence items to be indented, to force them not
to be indented, or don't care, respectively.
