bbp_remove_group_id_from_all_forums( type $group_id )

function bbp_remove_group_id_from_all_forums( $group_id = 0 ) {

	// Use current group if none is set
	if ( empty( $group_id ) )
		$group_id = bp_get_current_group_id();

	// Get current group IDs
	$forum_ids = bbp_get_group_forum_ids( $group_id );

	// Loop through forums and remove this group from each one
	foreach ( (array) $forum_ids as $forum_id ) {
		bbp_remove_group_id_from_forum( $group_id, $forum_id );
	}
}