remove watchdog-mux.socket

remove watchdog-mux.socket

The use of an systemd socket unit for the watchdog socket is not
necessary for us it even generates problems as the socket already
runs and accepts input when the watchdog-mux daemon itself is not
running. So the LRM/CRM could successfully open and update the
watchdog even if it was not running!

This patch removes the unit file, adds a postinst script which
handles the removal of the links generated from systemd itself
and removes also the code from watchdog-mux which handled
the systemd socket unit.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>