Revert "Mark tst_license as insignificant"

most repositories are already updated, let's reduce the
risk of files being merged with the wrong license header
by reverting this temporary change

This reverts commit 6076203fd3784d871b7b9b3e2d804660d59fcb2d.

Change-Id: Ifbac88f55384763cb34fd959a63981158fe17b53
Reviewed-by: Jani Heikkinen <jani.heikkinen@theqtcompany.com>
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>