bp_notifications_delete_notifications_on_user_delete( int $user_id )

function bp_notifications_delete_notifications_on_user_delete( $user_id ) {
	return BP_Notifications_Notification::delete( array(
		'user_id'           => $user_id,
		'item_id'           => false,
		'secondary_item_id' => false,
		'component_action'  => false,
		'component_name'    => false,
	) );
}