audio: Use 'sdk_version' instead of 'platform_apis'

Replace 'platform_apis: true' with 'sdk_version: module_current'.
The former causes compiling against SDK source code,
this is not needed for the audio HAL.

Bug: 205884982
Test: m android.hardware.audio.service-aidl.example
Change-Id: I9b9c32707ac7276f5cd077681bd1f8122bc20feb