[BUGFIX] Remove gap underneath Linkvalidator tabs

In Linkvalidator backend module the gap between tabs
and table is removed.

Change-Id: Icaed87594cb7e9833810709fd3ae9acf40b963f7
Resolves: #49997
Related: #49133
Releases: 6.2
Reviewed-on: https://review.typo3.org/22276
Reviewed-by: Felix Kopp
Tested-by: Felix Kopp