grl-acoustid: Remove unnecessary variable release_group_id
grl-acoustid: Remove unnecessary variable release_group_id

Earlier same variable release_group_id was assigned to both album id
and release group id.
Assign release group id and album id seperately with checks for their
corresponding keys instead of using same value for both of them

GNOME/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,GNOME/grilo-plugins