headers: Remove some left-over license text

Remove some left-over from commit e2be04c7 ("License cleanup: add SPDX
license identifier to uapi header files with a license")

When the SPDX-License-Identifier tag has been added, the corresponding
license text has not been removed.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Alexander Duyck <alexanderduyck@fb.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/88410cddd31197ea26840d7dd71612bece8c6acf.1663871981.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Jakub Kicinski <kuba@kernel.org>