systemd: remove workaround for lvm2-monitor.service's ExecStop line

systemd: remove workaround for lvm2-monitor.service's ExecStop line

Bug https://bugzilla.redhat.com/show_bug.cgi?id=843587 is handled better
now - the hang does not occur anymore. There are still error messages
issued though during shutdown if someone stops lvm2-lvmetad.service
manually that lvm2-monitor.service depends on (even during shutdown).
These errors are correct though and will point to incorrect
configuration (still having use_lvmetad=1 in lvm.conf and stopping
lvm2-lvmetad.service manually).

The workaround to prevent the hang is not needed now. So the
'--config "global{use_lvmetad=0}"' is now removed from the
lvm2-monitor.service's ExecStop line.