shadow: Remove local subid support as it was merged in oe-core

Merged in oe-core, kirkstone 5cdc9c1809ef169b8af7ce3085f316d1e68eb7ec.
This revision is included in the last oe-core bump.

Related to eclipse/oniro-core/oniro#772



Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>