REST API: Remove unused variable in WP_REST_Server::match_request_to_handler().

Previously initialized in `WP_REST_Server::dispatch()`, the `$response` variable became unused when the logic was split into two new methods, `::match_request_to_handler()` and `::respond_to_request()`.

Follow-up to [34928], [48947].

Props upadalavipul, mukesh27.
Fixes #59420.

git-svn-id: https://develop.svn.wordpress.org/trunk@56645 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -1079,7 +1079,6 @@ class WP_REST_Server {
 
 			foreach ( $handlers as $handler ) {
 				$callback = $handler['callback'];
-				$response = null;
 
 				// Fallback to GET method if no HEAD method is registered.
 				$checked_method = $method;