Only return one mobile subscription per group in Settings.

Right now getSelectableSubscriptionInfoList returns all subscriptions
that are visible and available. But we should only show one per
subscription group. So updating getSelectableSubscriptionInfoList
to make sure of it.

Bug: 126438122
Test: manual - group Fi primary subscriptions and make sure only
one Fi subscription is shown in Settings UI.
Change-Id: I867296b4f8efbdf2e9885ef34dd45806fa0abbca
Merged-In: I867296b4f8efbdf2e9885ef34dd45806fa0abbca