Part of #9744

Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

- Merge 'isinstance' calls.
- Remove unnecessary dict call outside of comprehension.
- Use 'sys.exit()' calls.

Replace every instance of `logger.warn` with `logger.warning` as the former is deprecated.