Apply fixes from StyleCI

Author: StyleCIBot

framework/core/src/Http/RequestUtil.php

@@ -11,7 +11,6 @@
 
 use Bitworking\Mimeparse;
 use Flarum\User\User;
-use Illuminate\Support\Str;
 use Psr\Http\Message\ServerRequestInterface as Request;
 use Tobyz\JsonApiServer\Exception\BadRequestException;