Revert "dispatcher/systemd: order NetworkManager-dispatcher.service Before=NetworkManager.service"

The 'Before' dependency between NM-dispatcher and NM causes a deadlock
when stopping the NM service. When terminating, NM wants to D-Bus
activate NM-dispatcher to synchronously handle pre-down events; but
NM-dispatcher start is ordered after NM shutdown due to the following
behavior described in systemd.unit(5) man page:

  Given two units with any ordering dependency between them, if one
  unit is shut down and the other is started up, the shutdown is
  ordered before the start-up. It doesn't matter if the ordering
  dependency is After= or Before=, in this case. It also doesn't
  matter which of the two is shut down, as long as one is shut down
  and the other is started up; the shutdown is ordered before the
  start-up in all cases.

So, NM is waiting NM-dispatcher to start and NM-dispatcher is queued
by systemd, waiting that NM is stopped. The result is a 90 seconds
delay, after which systemd kills NM and continues.

The dependency was added so that during shutdown NM-dispatcher would
be stopped after NM. I don't think it worked as expected because
NM-dispatcher is not supposed to be active most of the times, and so
it doesn't need a dependency that delays its stop after NM.

This reverts commit acc335aad4.

data/NetworkManager-dispatcher.service.in

@@ -1,12 +1,6 @@
 [Unit]
 Description=Network Manager Script Dispatcher Service
 
-# Order the dispatcher before NetworkManager. While dispatcher
-# is D-Bus activate (and not intended to be explicitly wanted by
-# another service/target), the ordering dependency matters during
-# shutdown. We want first NetworkManager to be stopped.
-Before=NetworkManager.service
-
 [Service]
 Type=dbus
 BusName=org.freedesktop.nm_dispatcher