Refactor factory_spec.rb to conform to Let's Not style

[richiethomas]

For reference:

https://thoughtbot.com/blog/lets-not

TL;DR- there is consensus within thoughtbot that RSpec's subject, before, and let features are over-used in the Ruby community, and result in relatively hard-to-read tests.

This is one of several PRs which in-lines many of the declarations previously made using the above idioms.

[composerinteralia]

I must have missed this one in my earlier reviews.

There might be some helper methods we can pull out later on, but lets merge for now to get rid of that pesky before block.