jobs: drop favgroup expunge job.

Make `Post#expunge!` remove favgroups synchronously.

app/models/favorite_group.rb

@@ -178,13 +178,6 @@ class FavoriteGroup < ApplicationRecord
     end
   end
 
-  def self.purge_post(post_id)
-    post_id = post_id.id if post_id.is_a?(Post)
-    for_post(post_id).find_each do |group|
-      group.remove!(post_id)
-    end
-  end
-
   def remove!(post_id)
     with_lock do
       post_id = post_id.id if post_id.is_a?(Post)

app/models/post.rb

@@ -1000,7 +1000,9 @@ class Post < ApplicationRecord
     end
 
     def remove_from_fav_groups
-      FavoriteGroup.delay.purge_post(id)
+      FavoriteGroup.for_post(id).find_each do |favgroup|
+        favgroup.remove!(id)
+      end
     end
   end