Remove superfluous ForbiddenException

It has the same effect as the PermissionDeniedException, so let's
just use that.

Refs #1641.

src/Extension/DefaultLanguagePackGuard.php

@@ -10,8 +10,8 @@
 namespace Flarum\Extension;
 
 use Flarum\Extension\Event\Disabling;
-use Flarum\Http\Exception\ForbiddenException;
 use Flarum\Settings\SettingsRepositoryInterface;
+use Flarum\User\Exception\PermissionDeniedException;
 use Illuminate\Support\Arr;
 
 class DefaultLanguagePackGuard
@@ -36,7 +36,7 @@ class DefaultLanguagePackGuard
         $locale = Arr::get($event->extension->extra, 'flarum-locale.code');
 
         if ($locale === $defaultLocale) {
-            throw new ForbiddenException('You cannot disable the default language pack!');
+            throw new PermissionDeniedException('You cannot disable the default language pack!');
         }
     }
 }

src/Foundation/ErrorServiceProvider.php

@@ -33,7 +33,6 @@ class ErrorServiceProvider extends AbstractServiceProvider
                 'invalid_access_token' => 401,
 
                 // 403 Forbidden
-                'forbidden' => 403,
                 'invalid_confirmation_token' => 403,
                 'permission_denied' => 403,
 

src/Http/Exception/ForbiddenException.php

@@ -1,21 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Http\Exception;
-
-use Exception;
-use Flarum\Foundation\KnownError;
-
-class ForbiddenException extends Exception implements KnownError
-{
-    public function getType(): string
-    {
-        return 'forbidden';
-    }
-}