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>`
The version of a module isn't going to change over the lifetime of the
process (assuming no funky hot reloading is going on, which it isn't),
so let's just cache the result to avoid spawning lots of git
subprocesses.
Fixes#5672.
