[BUGFIX] Clear cache system icon is shown for non admin in dev context

If the context is in development mode, the clear cache system icon
is always shown in the toolbar, even if the user is not an admin.

Resolves: #72964
Releases: master, 7.6, 6.2
Change-Id: I674df49fee14ded4b2190cca098ddf146047e5f0
Reviewed-on: https://review.typo3.org/46264


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>