lxdm: fix postinst-code

lxdm: fix postinst-code

Exiting postinst code leaves systemd.bbclass offline postinst code unexecuted,
causes postinst not to finish at first boot (lxdm.service is not aliased to
display-manager.service -> started much too early) and is not neccesary:
language preparation can be done offline.

(From meta-openembedded rev: defabe7408915c10b6df520247fa966ad0260846)

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>