While at it, also remove unnecessary "#!/usr/bin/env python3" in files
that only get imported, and adjust other empty/comment lines in the
beginnings of the files for consistency.
This makes files easier to read, and makes the pmbootstrap codebase more
consistent with the build.postmarketos.org codebase.
Remove a legacy code path from back in the day, where pmaports were in
the same repository as pmbootstrap ([1]). Nowadays, pmaports are always in a
git repository, so this is not necessary anymore. If git fails at this
point, crash hard and don't carry on with an empty string.
This is in preparation for using rev_parse in new code paths, so we
don't need to check the return value of rev_parse.
[1] 39548835 "Write custom os-release (closes#324) (#439)"
https://github.com/postmarketOS/pmbootstrap/pull/439
* Write custom os-release (closes#324)
* Return empty string instead of crashing when the directory is not a git repository
* Use https in homepage URL
