Revert "core: do not spawn jobs or touch other units during coldplugging"

This reverts commit 6e392c9c45.

We really shouldn't invent external state keeping hashmaps, if we can
keep this state in the units themselves.

src/core/device.c

@@ -140,7 +140,7 @@ static void device_set_state(Device *d, DeviceState state) {
         unit_notify(UNIT(d), state_translation_table[old_state], state_translation_table[state], true);
 }
 
-static int device_coldplug(Unit *u, Hashmap *deferred_work) {
+static int device_coldplug(Unit *u) {
         Device *d = DEVICE(u);
 
         assert(d);