Rather than deleting the source package and running the test suite from the
project root, move the tests to the temporary installation and run the suite
from there.

Todo: https://archlinux.org/todo/stop-using-python-setuppy-test/

Other changes:

- Use SPDX license identifier.
- Add implicitly satisfied dependencies reported by namcap.

Had tested manually in a chroot, but failed to notice `python -m
unittest` only worked after I had run `python setup.py test`.

(I had forgotten to copy over the `python_version` variable
initialization, but that's irrelevant.)

fix test failures with new gammu version

FTR, commands used to change arch=() and then verify the changes:

$ sed -Ei "/^arch=/{s/ *?['\"]?i686['\"]? *?//;s/ *$//}" */*/PKGBUILD*

$ grep -r i686 * | grep arch= | grep -v repos

$ svn diff | grep -A 1 ^-[^-] | grep -v -- -- | cut -c2- |
  while IFS=$'\n' read -r l1; IFS=$'\n' read -r l2; do
    echo "$l1 -> $l2"
  done | sort -u