Remove File Type Override

Remove file type overwrite previously used to force downloads. This
addresses potential XSS where an attacker could pass "image" resulting in
the file being displayed in line.

include/class.file.php

@@ -247,8 +247,6 @@ class AttachmentFile extends VerySimpleModel {
         $ttl = ($expires) ? $expires - Misc::gmtime() : false;
         $this->makeCacheable($ttl);
         $type = $this->getType() ?: 'application/octet-stream';
-        if (isset($_REQUEST['overridetype']))
-            $type = $_REQUEST['overridetype'];
         Http::download($this->getName(), $type, null, 'inline');
         header('Content-Length: '.$this->getSize());
         $this->sendData(false);