[!!!][TASK] Remove setting config.uniqueLinkVars

The setting *config.uniqueLinkVars* is removed as the
behaviour is now always used.

Resolves: #62888
Releases: master
Change-Id: I016cc74a6f4e450dcfc7678bca5ef6cfcb066be6
Reviewed-on: http://review.typo3.org/34021
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>