Move asnyc call audio tasks to single thread. am: 77334881 am: f5a125b0

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/services/Telecomm/+/23917454



Change-Id: I0420129b6c330334b27e6fb30dd64e5446fe907a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>