do not use Accept-Encoding in browser UID

Since Chrome 37, they send differen accept encodings for POST and GET
requests which will break BrowserUID checks as reported in
cosmocode/dokuwiki-plugin-oauth/issues/3

See https://code.google.com/p/chromium/issues/detail?id=410559 for
official bug report at Google

inc/auth.php

@@ -335,7 +335,6 @@ function auth_browseruid() {
     $ip  = clientIP(true);
     $uid = '';
     $uid .= $INPUT->server->str('HTTP_USER_AGENT');
-    $uid .= $INPUT->server->str('HTTP_ACCEPT_ENCODING');
     $uid .= $INPUT->server->str('HTTP_ACCEPT_CHARSET');
     $uid .= substr($ip, 0, strpos($ip, '.'));
     $uid = strtolower($uid);