The nimbusStore feature has been removed because all of its features are now default-on. The prefs that determine whether the NimbusEnrollments table are used still exist due to xpcshell tests, where we cannot easily enable the ProfilesDatastoreService in all cases. These prefs are already enabled inside Nimbus' own xpcshell tests. Differential Revision: https://phabricator.services.mozilla.com/D297469