Drop product FK from Topic

[akatsoulas]

No description provided.

[escattone]

Oops, I missed a couple of things in my first review:

• The Topic.documents method uses self.product (

  kitsune/kitsune/products/models.py

  Line 159 in 87448ca

  "products": self.product,

  ). I'm thinking that line should be "products__in": self.products, instead?
• The Topic.__str__ method also uses self.product (

  kitsune/kitsune/products/models.py

  Line 133 in 87448ca

  if self.product:

  ). I'm thinking lines 133-134 can be removed?