[TASK] Code and comment clean up

There are several places with typos, or wrong comments.

Additionally, some places still contain a check for PATH_site which dates
back to TYPO3 versions before a clean bootstrap was in place, and
where strict checks in conditions were forgotten.

Resolves: #81031
Releases: master, 8.7
Change-Id: I44e4f1647c52d0eaa843664b08cd05d56ab66aaf
Reviewed-on: https://review.typo3.org/52626


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Henrik Elsner <helsner@dfau.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>