BuddyPress.org

Since the child theme functions.php loads first you have to add an action that removes the other action before it tries to execute it. Since the core action runs at default priority 10, you just have to hook in at priority 9.

Here is how to do it:

function remove_header_support() {

remove_action( 'init', 'bp_dtheme_add_custom_header_support' );

}

add_action( 'init', 'remove_header_support', 9 );