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/socket.c

@@ -1323,7 +1323,7 @@ static void socket_set_state(Socket *s, SocketState state) {
         unit_notify(UNIT(s), state_translation_table[old_state], state_translation_table[state], true);
 }
 
-static int socket_coldplug(Unit *u, Hashmap *deferred_work) {
+static int socket_coldplug(Unit *u) {
         Socket *s = SOCKET(u);
         int r;