Remove leaudio_callback_on_group_stream_status flag

Bug: 323288188
Bug: 323288608
Test: atest BluetoothLeAudioTest; atest LeAudioServiceTest;
atest --host bluetooth_le_audio_client_test
Flag: com.android.bluetooth.flags.leaudio_callback_on_group_stream_status

Change-Id: Icb7a3ca2d4caa5277488da69f56408b0aa9d986f