If old theme is already using a custom meta function, then we want to unhook the new options for sub meta.

unhook-new-sub-meta-options.php

<?php
/**
 * Remove Content > Single > Sub Meta Information
 */
themeblvd_remove_option( 'content', 'single', 'single_sub_meta' );

/**
 * Remove Sub Meta Information option from Post Options
 */
function theme_remove_sub_meta_post_option( $setup ) {
	unset($setup['tb_sub_meta']);
	return $setup;
}
add_filter( 'themeblvd_post_meta', 'theme_remove_sub_meta_post_option' );