[TASK] Remove checkSimilar property in DataHandler

The internal property $this->checkSimilar is always
true and never set differently. It can be removed
from the codebase.

Resolves: #100052
Releases: main
Change-Id: I8c224d91f8866822d64e5a1b0de136ba256d6072
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77988


Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>