No need to mutate metadata for `render_views` state.

Mutating metadata is problematic so using an ivar is better.

Also, remove a deprecated API while we're at it.
Don't mutate `described_class` metadata.

Just set the controller class instead. Mutating
metadata has some odd edge case bugs (as rspec-core
doesn't update it's filters/hooks/etc when metadata
is mutated), so it's best to avoid it.
No need to infer spec type in our spec_helper.