remove unused RangeTreeIndex route, fixes #4397

Closes #4397

Merge request studip/studip!3280

lib/classes/JsonApi/Routes/RangeTree/RangeTreeIndex.php

-<?php
-
-namespace JsonApi\Routes\RangeTree;
-
-use Psr\Http\Message\ServerRequestInterface as Request;
-use Psr\Http\Message\ResponseInterface as Response;
-use JsonApi\Errors\AuthorizationFailedException;
-use JsonApi\Errors\RecordNotFoundException;
-use JsonApi\JsonApiController;
-
-/**
- * Zeigt eine bestimmte Veranstaltung an.
- */
-class RangeTreeIndex extends JsonApiController
-{
-
-    protected $allowedIncludePaths = [
-        'children',
-        'courses',
-        'institute',
-        'parent',
-    ];
-    protected $allowedPagingParameters = ['offset', 'limit'];
-
-    /**
-     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
-     */
-    public function __invoke(Request $request, Response $response, $args)
-    {
-        $tree = \TreeAbstract::getInstance('StudipSemTree', ['visible_only' => 1]);
-        $studyAreas = self::mapTree('root', $tree);
-        list($offset, $limit) = $this->getOffsetAndLimit();
-
-        return $this->getPaginatedContentResponse(
-            array_slice($studyAreas, $offset, $limit),
-            count($studyAreas)
-        );
-    }
-
-    private function mapTree($parentId, &$tree)
-    {
-        $level = [];
-        $kids = $tree->getKids($parentId);
-        if (is_array($kids) && count($kids) > 0) {
-            foreach ($kids as $kid) {
-                $level[] = \StudipStudyArea::find($kid);
-                $level = array_merge($level, self::mapTree($kid, $tree));
-            }
-        }
-
-        return $level;
-    }
-}