AudioService: fix volume group setting name

The setting name for a volume group must also be updated
when the corresponding public stream setting name is changed.
Also no need to persist the volume group index when there is a
corresponding public stream as this is redundant.

Bug: 270815307
Test: repro steps in bug
Test: ates AudioManagerTest

Change-Id: I4edc8036201cba1fb7f79f12f434a871f6010114