[TASK] Remove unused helper_javascript_css.html template file

typo3/sysext/backend/Resources/Private/Templates/helper_javascript_css.html
is an unused left over since FormEngine rewrite in v7 and can be dropped.

Resolves: #94226
Releases: master
Change-Id: Ic8eccade663e380c37f9abb045f14c3a5992adb4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69313


Tested-by: core-ci <typo3@b13.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Christian Wolff <chris@wolffc.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Wolff <chris@wolffc.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>