Refactor note removal

Remove the note removal code from *_delete()/*_erase() and create a new
wrapper function called day_item_erase_note() that is be used to drop
the note being associated to an item.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/event.c

@@ -158,9 +158,6 @@ void event_delete(struct event *ev, enum eraseflg flag)
     EXIT(_("no such appointment"));
 
   switch (flag) {
-  case ERASE_FORCE_ONLY_NOTE:
-    erase_note(&ev->note);
-    break;
   case ERASE_CUT:
     LLIST_REMOVE(&eventlist, i);
     break;