Remove FactoryGirl.lint in before(:suite)

We estimate that `lint`ing adds an extra ~300ms on a typical app we work
on for every `rspec` run, even a focused test that only runs one spec.
Until we can find a way to avoid paying that penalty, the discussion
below has landed at not putting it in Suspenders:

https://github.com/thoughtbot/suspenders/pull/299/files#r10642936