Part of T101073: after the view layer sync was made lazy (D15885), the
BKE_layer_collection_resync_forbid and BKE_layer_collection_resync_allow
in Alembic/USD/OBJ importers is no longer needed, as long as they do
view layer dependent operations (selecting new objects) in a separate
loop after creating all the objects.
Verified that this does not regress import times for 26k objects OBJ
scene (Blender 3.0 splash) and 250k objects USD scene (Moana).
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