[TASK] Update comments in ExtensionManagementUtility

Comments now mention that functions in ExtensionManagementUtility
must not be used in ext_tables.php

Resolves: #80837
Releases: master, 8.7
Change-Id: Ib36bdb1b6b6cc055759498199931f09b03065ebe
Reviewed-on: https://review.typo3.org/52437


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>