bp_media_messages_delete_attached_media( $thread_id,  $message_ids )

function bp_media_messages_delete_attached_media( $thread_id, $message_ids ) {

    if ( ! empty( $message_ids ) ) {
        foreach( $message_ids as $message_id ) {

            // get media ids attached to message
	        $media_ids = bp_messages_get_meta( $message_id, 'bp_media_ids', true );

	        if ( ! empty( $media_ids ) ) {
		        $media_ids = explode( ',', $media_ids );
                foreach( $media_ids as $media_id ) {
                    bp_media_delete( $media_id );
                }
            }
        }
    }
}