LeAudio: Minor broadcast configuration cleanup

 - removed the unused bitrate
 - adjusted the parameter naming to match the BT specification

Bug: 295972694
Test: atest --host bluetooth_le_audio_test bluetooth_le_audio_client_test bluetooth_test_broadcaster bluetooth_test_broadcaster_state_machine bluetooth_le_audio_codec_manager_test
Change-Id: I6d9f869d32bc6ebf970759f3e71e54227e25851c