Fix defect db migration

Follow-up to fc999c04b3

db/post_migrate/20190205104116_drop_unused_auth_tables.rb

@@ -2,17 +2,6 @@ require 'migration/table_dropper'
 
 class DropUnusedAuthTables < ActiveRecord::Migration[5.2]
   def change
-    def up
-      %i{
-        facebook_user_infos
-        twitter_user_infos
-      }.each do |table|
-        Migration::TableDropper.execute_drop(table)
-      end
-    end
-
-    def down
-      raise ActiveRecord::IrreversibleMigration
-    end
+    # this migration was defect
   end
 end

db/post_migrate/20190208144706_drop_unused_auth_tables_again.rb

@@ -0,0 +1,16 @@
+require 'migration/table_dropper'
+
+class DropUnusedAuthTablesAgain < ActiveRecord::Migration[5.2]
+  def up
+    %i{
+        facebook_user_infos
+        twitter_user_infos
+      }.each do |table|
+      Migration::TableDropper.execute_drop(table)
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end