[security] SubscriptionGroup is exposed to unprivileged callers

SubscriptionInfo.mGroupUUID is not cleared in
conditionallyRemoveIdentifiers if the caller only has READ_PHONE_STATE
(based on a check to checkReadPhoneState) and not READ_DEVICE_IDENTIFIERS.
Bug: 181053462
Test: atest SubscriptionManagerTest

Change-Id: Ic2b62523330dc6e2169ad851715c4ab3da3b29cf