Remove outdated workaround for operationName and operation

This should not be needed since webonyx/graphql-php#256

This is a breaking change only if you rely on the existing of `operation`
instead of `operationName` in subsequent middleware. It is not breaking
if you only use `GraphQL\Server\StandardServer`.

Fixes #7

Author: PowerKiKi

src/UploadMiddleware.php

@@ -56,10 +56,6 @@ private function parseUploadedFiles(ServerRequestInterface $request): ServerRequ
 
         $map = json_decode($bodyParams['map'], true);
         $result = json_decode($bodyParams['operations'], true);
-        if (isset($result['operationName'])) {
-            $result['operation'] = $result['operationName'];
-            unset($result['operationName']);
-        }
 
         foreach ($map as $fileKey => $locations) {
             foreach ($locations as $location) {