Files which are installed as-is (any .service and other unit files, .conf
files, .policy files, etc), are left as is. My assumption is that SPDX
identifiers are not yet that well known, so it's better to retain the
extended header to avoid any doubt.
I also kept any copyright lines. We can probably remove them, but it'd nice to
obtain explicit acks from all involved authors before doing that.
The script wasn't apparently used since the switch to meson, because
it required the sys subdirectory to be present in the same subdirectory
where the output script is located.
Let's use f-strings to make the whole thing more readable. Add some
extra checks.
This is useful on systems like NixOS, where python3 is not in
/usr/bin/python3 as well as for people using alternative ways to
install python such as virtualenv/pyenv.
The script contains the contents of all sys/ test files, and creates
all dirs/links/files when run. This replaces the sys.tar.xz tarball
that contained sys/, so changes to sys files only require a simple
commit in git, instead of checking in an entire new tarball for each
sys/ change.
