Revert "SoundPool: Use caller thread for sound playback"

This reverts commit 66262b16fb169676d768a8be52485881ea53da54.

Reason for revert: < CL will be reverted since we are seeing a memory  regression. Please refer this bug http://b/145834064. Exempt-From-Owner-Approval: see go/perf-revert-firs>

Change-Id: I42db74b5e65f6cdc88d69bfbb686c93620ee563c
1 file changed