Revert "[bug 893328] Related articles should have same product"

This reverts commit 8908f4b794e026d41c77968eef47d2f093754114.

This causes the _mlt queries to fail on prod.
Need to figure it out.
Revert "Revert "[bug 893328] Related articles should have same product""

This reverts commit bfd73ec54a3189f2cacd5211b372006ed75b575c.
Tweak related_documents to use correct products.