Audio VNDK: remove legacy HAL shim

The audio shim were never intended to be part of the VNDK,
they are not ABI stable (as they are a shim to a non ABI stable legacy
API) and provide no value as are just a set of simple helper functions.

Bug: 118203066
Test: compile
Change-Id: Ie6f14dc314c46cf8f29ba8dfd872942cda78bca8
Signed-off-by: Kevin Rocard <krocard@google.com>