Revert "Make SubscriptionManager.getSlotIndex public"

This reverts commit ccea7355fdcbc2a31e46bd1f26d784811062ac51.

Reason for revert: broke some esim usage (bug#116861976)

Change-Id: I8e6debac959460954ba4c16ef4c0e2ebcc68b5ec
Bug: 116861976
Bug: 113072551
2 files changed