Reverse removal of link_to_remove helper

There was a patch submitted to fix a no method error with link_to_remove when trying to edit a product's ad-hoc option types, issue #52.

The latest commits to upgrade to spree 1.3 removed this fix.  However, the error seems to have recurred because of it.

I added the file back and tested on 1.3-stable.  It works for me, I went through the whole process of editing ad-hoc option types.  So I'm submitting this pull request.