AudioService: default volume group is not restored

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

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

Change-Id: I00aa8c17bffca21a128086fbbbeafffc26521a3b
Merged-In: I239145d8bc50237ff902026594423c6d1fa04ad4