selinux: drop mac_selinux_unit_access_check_strv()

selinux: drop mac_selinux_unit_access_check_strv()

It is not acceptable to load unit files during enable/disable operations
just to figure out the selinux labels. systemd implements lazy loading
for units, so the selinux hooks need to follow it.

This drops the mac_selinux_unit_access_check_strv() helper which
implements a non-acceptable policy check. If anyone cares for that
functionality, you really should pass a callback+userdata to the helpers
in src/shared/install.c which does policy checks on each touched file.

See #1050 on github for more.