SF: Clean up display lookup

Remove redundant functions. Phase out the "internal display" misnomer,
which is confusing for foldables.

Validate the DisplayPrimaries API against the connection type, rather
than the active display.

Bug: 182939859
Bug: 74619554
Test: Boot and fold/unfold
Change-Id: Ibe69e3337806a3f269f355522bcf65eab974d7bb