[BUGFIX] Wrong usage of array_unique()

RootlineUtility.php does not use return value of array_unique() call,
which makes the call ineffective.

This causes some huge SQL queries and increases page load time heavily.

Resolves: #46000
Releases: 6.1, 6.0
Change-Id: Ic614a22a97927cc433eab9e5bf1b6125d53b5882
Reviewed-on: https://review.typo3.org/18691
Reviewed-by: Michael Stucki
Tested-by: Michael Stucki
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Dmitry Dulepov
Tested-by: Dmitry Dulepov