Remove useless recursion in DeckManager.rem

For any deck the children of it's children are its children. So
applying rem to children of children is useless and actually slightly
costly for deep subdecks

pylib/anki/decks.py

@@ -150,13 +150,13 @@ class DeckManager:
             self.col.sched.emptyDyn(did)
             if childrenToo:
                 for name, id in self.children(did):
-                    self.rem(id, cardsToo)
+                    self.rem(id, cardsToo, childrenToo=False)
         else:
             # delete children first
             if childrenToo:
                 # we don't want to delete children when syncing
                 for name, id in self.children(did):
-                    self.rem(id, cardsToo)
+                    self.rem(id, cardsToo, childrenToo=False)
             # delete cards too?
             if cardsToo:
                 # don't use cids(), as we want cards in cram decks too