Sitemaps: Remove superfluous ? from rewrite rule.

Props szepeviktor.
Fixes #63699.

git-svn-id: https://develop.svn.wordpress.org/trunk@60458 602fd350-edb4-49c9-b593-d223f7449a82

Author: swissspidy

src/wp-includes/class-wp-rewrite.php

@@ -1288,7 +1288,7 @@ public function rewrite_rules() {
 		$favicon_rewrite = ( empty( $home_path['path'] ) || '/' === $home_path['path'] ) ? array( 'favicon\.ico$' => $this->index . '?favicon=1' ) : array();
 
 		// sitemap.xml -- only if installed at the root.
-		$sitemap_rewrite = ( empty( $home_path['path'] ) || '/' === $home_path['path'] ) ? array( 'sitemap\.xml' => $this->index . '??sitemap=index' ) : array();
+		$sitemap_rewrite = ( empty( $home_path['path'] ) || '/' === $home_path['path'] ) ? array( 'sitemap\.xml' => $this->index . '?sitemap=index' ) : array();
 
 		// Old feed and service files.
 		$deprecated_files = array(