Deletes a post meta field for the given post ID.

You can match based on the key, or key and value. Removing based on key and
value, will keep from removing duplicate metadata with the same key. It also
allows removing all metadata matching the key, if needed.

function delete_post_meta( $post_id, $meta_key, $meta_value = '' ) {
	// Make sure meta is deleted from the post, not from a revision.
	$the_post = wp_is_post_revision( $post_id );
	if ( $the_post ) {
		$post_id = $the_post;
	}

	return delete_metadata( 'post', $post_id, $meta_key, $meta_value );
}