unstick_post( int $post_id )

function unstick_post( $post_id ) {
	$stickies = get_option('sticky_posts');

	if ( !is_array($stickies) )
		return;

	if ( ! in_array($post_id, $stickies) )
		return;

	$offset = array_search($post_id, $stickies);
	if ( false === $offset )
		return;

	array_splice($stickies, $offset, 1);

	$updated = update_option( 'sticky_posts', $stickies );

	if ( $updated ) {
		/**
		 * Fires once a post has been removed from the sticky list.
		 *
		 * @since WP-4.6.0
		 *
		 * @param int $post_id ID of the post that was unstuck.
		 */
		do_action( 'post_unstuck', $post_id );
	}
}