AudioService: default volume group is not restored

Volume Group with associated stream type does not have their volume
restored after restart / crash even if correctly stored in
Settings DB.
A guard prevents from restoring it. However, when using volume per attributes,
Settings DB is used, so it is safe to restore volumes for all groups.
This CL fixes this issue by removing this guard.

Bug: 136121584
Test: set Music volume & reboot & dumpsys audio
    Ensure indexes matches
Signed-off-by: Francois Gaffie <francois.gaffie@renault.com>

Change-Id: I00aa8c17bffca21a128086fbbbeafffc26521a3b