[BUGFIX] Accessibility bypass in dt for menu with abstract

The TypoScript path of the accessiblity bypass has changed so the
code that overrides the wrapping <li> with a <dt> element is adapted
to match the new TypoScript path.

Resolves: #57712
Releases: master, 6.2
Change-Id: Ib0347ddae6091792b85ee77133db8d711982a12b
Reviewed-on: http://review.typo3.org/34962
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>