autofs: Remove systemd related things.

* Autofs was being inherited from systemd. This class is only
present in meta-systemd. So bitbake was giving parse error
about systemd class. So removed systemd from inherit and
removed SYSTEMD_PACKAGES and SYSTEMD_SERVICE.

Signed-off-by: Noor Ahsan <noor_ahsan@mentor.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>