audio_hal_interface/aidl/a2dp: Remove BluetoothAudioCtrlAck

This enum was added to shim the type from the aidl interface;
the type BluetoothAudioStatus from bluetooth::audio::a2dp
now can be used directly.

Test: m com.android.btservices
Flag: EXEMPT, no logical change
Bug: 365022887
Change-Id: I9070390383c7a2aaa4755e57b3745c2f1296442e