Fix APS death notification

Our death recipient object was being kept alive only by the reference
held by the remote process, the one we want the death notifications
from. When it dies, we have a race condition between the death call
and the listener being garbage collected.

Furthermore, since the global APS reference may get replaced by a new
one as part of clearAudioConfigCache(), we keep the old reference
around, or else our death listener becomes invalidated silently.

Fixes: 165780067
Test: Manual verification of sound trigger recovery after killing
      audioserver multiple times, while generating touch sounds.
Change-Id: If24c59ec3e3d01f418fbf575b8cc32ae0ba7fa2e