[TASK] Remove underline in pagetree

The underline that appears after clicking a page in
pagetree gets removed.

Resolves: #63198
Releases: master
Change-Id: I919158458d0e51db819d09fe60cbf2cf472e403c
Reviewed-on: http://review.typo3.org/34770
Reviewed-by: Felix Kopp <felix-source@phorax.com>
Tested-by: Felix Kopp <felix-source@phorax.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>