REST API: Remove redundant "0" parameter.

This is just an artifact of how we parse the URL, and is already available
via $request->get_route()

Props danielbachhuber.
Fixes #34647.


git-svn-id: https://develop.svn.wordpress.org/trunk@35659 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -789,6 +789,8 @@ class WP_REST_Server {
 				}
 
 				if ( ! is_wp_error( $response ) ) {
+					// Remove the redundant preg_match argument.
+					unset( $args[0] );
 
 					$request->set_url_params( $args );
 					$request->set_attributes( $handler );