[pm] do not send UID_REMOVED broadcast if shared uid still exists

Fixing a regression from ag/25622404. When the UID is still shared with
other apps, don't send UID_REMOVED broadcast when an app is removed.

BUG: 320657384
Test: atest
android.content.pm.cts.PackageManagerTest#testUidRemovedBroadcastNotReceivedForSharedUid

Change-Id: Ie2d91fa7e85063b2cd929c9d62928d96f7902fe4