[!!!][TASK] Remove deprecated PHP classes from EXT:core

The following previously deprecated PHP classes are now removed:
- TYPO3\CMS\Core\Encoder\JavaScriptEncoder
- TYPO3\CMS\Core\Resources\Utility\BackendUtility
- TYPO3\CMS\Core\Utility\ClientUtility
- TYPO3\CMS\Core\Utility\PhpOptionsUtility

Resolves: #87201
Releases: master
Change-Id: I0b1896692ebf1f15948a9a3661fdc10ab6f019ff
Reviewed-on: https://review.typo3.org/59195


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>