headers: Remove some left-over license text

Remove a left-over from commit 2874c5fd

 ("treewide: Replace GPLv2
boilerplate/reference with SPDX - rule 152")

There is no need for an empty "License:".

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/0e5ff727626b748238f4b78932f81572143d8f0b.1662896317.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>