WordPress at a glance
function is not described

unregister_post_meta() WP 4.9.8

Unregisters a meta key for posts.

No Hooks.

Return

true/false. True on success, false if the meta key was not previously registered.

Usage

unregister_post_meta( $post_type, $meta_key );
$post_type(string) (required)
Post type the meta key is currently registered for. Pass an empty string if the meta key is registered across all existing post types.
$meta_key(string) (required)
The meta key to unregister.

Code of unregister post meta: wp-includes/post.php VER 5.1.1

<?php
function unregister_post_meta( $post_type, $meta_key ) {
	return unregister_meta_key( 'post', $meta_key, $post_type );
}