Assuming we won't need this anymore in 68+ release, we can clean up locale-specific selecting logic. This probably wants to happen after bug 1552280. Although potentially depending on the decision there, we might end up re-purposing some of the experimentation logic to randomly pick a triplet.
Notably, we shouldn't need the enrollment ping bug 1549784 nor pref for survey bug 1549846.
More generally, we should work with normandy to figure out a more reusable experimentation framework for firstrun experiments.