pid1: convert to the new scheme

In all the other cases, I think the code was clearer with the static table.
Here, not so much. And because of the existing dump code, the vtables cannot
be made static and need to remain exported. I still think it's worth to do the
change to have the cmdline introspection, but I'm disappointed with how this
came out.

src/core/timer.c

@@ -925,6 +925,5 @@ const UnitVTable timer_vtable = {
         .time_change = timer_time_change,
         .timezone_change = timer_timezone_change,
 
-        .bus_vtable = bus_timer_vtable,
         .bus_set_property = bus_timer_set_property,
 };