[BUGFIX] Replace mentions of index_ts.php

The file index_ts.php is now \TYPO3\CMS\Frontend\Http\RequestHandler,
this change replaces all mentions of the old file.

Resolves: #72720
Releases: master, 7.6
Change-Id: Ic35c29b465d8d5f7d495591c9420b94147fb0a3f
Reviewed-on: https://review.typo3.org/45924


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>