Remove unique_hash column in uc_products table

I don't think it is used any more. Maybe it should be removed, it might be useful to uniquely identify a product, but UUID module is probably better for this.

Yeah, that's a leftover from Drupal 5 / Ubercart 1, which used to have a built-in uc_importer module to do XML import/export of products. They needed a unique identifier for products that would work across different machines - nid is the primary key for the table but nids are machine-specific. You can read more about it if you're interested by searching ubercart.org: http://www.ubercart.org/search/node/unique_hash

Product import/export is best done these days through a general purpose module that can deal with all types of nodes, not just products. I'm not sure why unique_hash wasn't removed 5 years ago; we've been unknowingly carrying it around for years and it's no longer needed.

Changing this to a task ...

The attached patch removes this column and all code that refers to it. The only thing that still used it was uc_product_uc_product_class() which used it as a way of identifying rows in uc_products without any data when converting an existing content type into a product class. There is a simpler way to do this in SQL, and I added a test to confirm this still works.

Committed #4.