Stop building the Python 2 bindings packages: python-apparmor, python-libapparmor (Closes: #904599).

1. They have no reverse-deps in Debian or Ubuntu.
2. I'd rather not encourage new software being written using the Python 2 bindings.
3. There's been 2 Debian stable releases with both Python 2 and Python 3 binding included, which should be enough to migrate. Stretch is still supported for a good while anyway.