remove unused and unneccesary user_id from taggings table.

this way we can stay closer to the defaults of has_many_polymorphs thus making upgrading easier

db/migrate/045_remove_user_from_taggings.rb.rb

@@ -0,0 +1,9 @@
+class RemoveUserFromTaggings < ActiveRecord::Migration
+  def self.up
+    remove_column :taggings, :user_id
+  end
+
+  def self.down
+    add_column :taggings, :user_id, :integer
+  end
+end