posts: don't move favorites to parent when expunging.

Don't automatically move favorites to the parent when expunging a post.
This can be done manually if necessary. Posts shouldn't have their
favorites moved unless they're duplicates, which expunged posts usually
aren't.

app/models/post.rb

@@ -973,7 +973,6 @@ class Post < ApplicationRecord
         Post.without_timeout do
           ModAction.log("permanently deleted post ##{id}", :post_permanent_delete)
 
-          give_favorites_to_parent
           update_children_on_destroy
           decrement_tag_post_counts
           remove_from_all_pools