[TASK] Cleanup ext:info and ext:info_pagetsconfig

- Remove require_once calls
- Replace global $LANG and $BACK_PATH
- Make some function calls use real boolean

Change-Id: I6e913e183a8357076b55d84c961e1104d643e81e
Resolves: #49992
Releases: 6.2
Reviewed-on: https://review.typo3.org/22271
Reviewed-by: Oliver Klee
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind