Environment Product Removal: fixing migration to work with FKs

Environment Product Removal - fixing the remove environment_products migration
to work correctly with the foreign keys change. Apparently postgres does not
support altering schema and changing data in the same transaction and rails
uses one transaction per migration so the former migration was split into 3
migrations.
Merge pull request #2614 from daviddavis/temp/1373480069

Environment Product Removal: fixing migration to work with FKs