rails/rails — pull request #12526 by hitendrasingh (2013-10-14 12:47:43+00:00)
Title: Remove unused HABTM builder and its autoload

As I could see https://github.com/rails/rails/commit/5864b9a894a784aea3500d7b72ab78b6f23c6fe9 that @tenderlove have removed the HABTM Support. So removing remaining HABTM code in builder.