aaudio: cleaned up PlayerBase implementation

Simplify registration. Reduce use of virtual methods.

This CL, plus some CLs in AudioManager, should fix
crashes involving RefBase::decStrong

Bug: 65450109
Test: CTS or "write_sine_callback -m2 -pl"
Change-Id: Ie1decd20f8d44bdefb0faf92e6b74de4f72e86bd
6 files changed