rootdir: init.rc: remove audio app/sys groups, merge to fg

With this change, the audio rr/fifo threads will just run in
the fg cgroup.

Also, the RR budget for the apps fg/bg threads has been bumped
to 80%. Ideally, the bg budget would be much smaller but there
are legacy libraries that seem to be very sensitive to this so
for now keep it at this value.

Bug: 6528015
Change-Id: I08f295e7ba195a449b96cd79d954b0529cee8636
Signed-off-by: Dima Zavin <dima@android.com>