AudioService: Remove STREAM_NOTIFICATION from ringer mode streams

Change-Id: Ie8d25743b27839fa2bd4e9ae5d3d0a49410ac5b4
JIRA: CYAN-344
Issue: https://jira.cyanogenmod.org/browse/CYAN-344
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>