headers: Remove some left-over license text in include/uapi/linux/dvb/

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.

Remove it now.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>