Revert [28894] as it's currently unused in core.

see #28487.

git-svn-id: https://develop.svn.wordpress.org/trunk@29309 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -3501,19 +3501,6 @@ function is_ssl() {
 	return false;
 }
 
-/**
- * Determine if the scheme of the given URL is https.
- *
- * @since 4.0.0
- * 
- * @param string $url The URL.
- * @return bool True if the given URL uses https, false if not (or if the URL
- *              is not valid).
- */
-function is_https_url( $url ) {
-	return ( 'https' === parse_url( $url, PHP_URL_SCHEME ) );
-}
-
 /**
  * Whether SSL login should be forced.
  *