Remove broken FactoryGirl.lint

This seems to have been broken in version 4.5 of factory_girl.
Most likely in this commit
https://github.com/thoughtbot/factory_girl/commit/f451e4a4193d7c2864b43e7cfa4d7ce699a65820.
It will hopefully be fixed in 4.6 and this line can be uncommented.
Merge pull request #143 from biola/remove_factory_girl_lint

Remove broken FactoryGirl.lint
Merge branch 'master' into remove_curriculum_string

* master:
  Remove broken FactoryGirl.lint