REST API: Remove unused variable `$api_root` from WP_Rest_Server->embed_links() method.

After [r36674] the variable `$api_root` is no longer used in this method and should be removed.

See #35803.

git-svn-id: https://develop.svn.wordpress.org/trunk@37021 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -520,7 +520,6 @@ class WP_REST_Server {
 		}
 
 		$embedded = array();
-		$api_root = rest_url();
 
 		foreach ( $data['_links'] as $rel => $links ) {
 			// Ignore links to self, for obvious reasons.