[TASK] Deprecate second argument of GeneralUtility::mkdir_deep()

The syntax is very confusing, and the second argument is not necessarily
needed - most of the TYPO3 Core code uses only the first argument.

In order to streamline the API the second method argument is deprecated
but still works as before.

Resolves: #82702
Releases: master
Change-Id: Ib2238ff90edf932f9410cf87c214e23d0a1c4826
Reviewed-on: https://review.typo3.org/54323


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>