debian: postinst: don't start systemd services

Starting services in the postinst script doesn't make much sense since
the package is normally installed in the template. In addition the start
can fail when executed through a trigger.

debian/qubes-core-agent.postinst

@@ -179,9 +179,7 @@ enableSystemdUnits() {
             #displayFailedStatus is-enabled ${unit}
         } || {
             echo "Enabling: ${unit}..."
-            systemctl enable ${unit} > /dev/null 2>&1 && {
-                systemctl start ${unit} > /dev/null 2>&1 || displayFailedStatus start ${unit}
-            } || {
+            systemctl enable ${unit} > /dev/null 2>&1 || {
                 echo "Could not enable: ${unit}"
                 displayFailedStatus enable ${unit}
             }