remove unused broken tag_count column

app/models/tag_group_membership.rb

@@ -1,4 +1,4 @@
 class TagGroupMembership < ActiveRecord::Base
   belongs_to :tag
-  belongs_to :tag_group, counter_cache: "tag_count" # TODO: remove counter cache
+  belongs_to :tag_group
 end

db/migrate/20160609203508_remove_tag_count_from_tag_groups.rb

@@ -0,0 +1,5 @@
+class RemoveTagCountFromTagGroups < ActiveRecord::Migration
+  def change
+    remove_column :tag_groups, :tag_count
+  end
+end