avahi: Don't remove users/groups in postrm

avahi: Don't remove users/groups in postrm

There's no way to ensure that files owned by the users aren't left
on the system at postrm time: Removing the user would mean those
files are now owned by a non-existing user, and later may be owned
by a completely unrelated new user.

[YOCTO #10442]

Signed-off-by: Jussi Kukkonen <jussi.kukkonen@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>