Remove redundant `setupTest` invocation.
Remove redundant `setupTest` invocation.

This resolves the error when using ember-destroyable-polyfill and
calling `setupContext` (from `@ember/test-helpers`) multiple times with
the same test context.

trentmwillis/ember-exam,trentmwillis/ember-exam,trentmwillis/ember-scatter,trentmwillis/ember-scatter,trentmwillis/ember-exam