platform: x86: get rid of a non-existent document

Changeset 163ede97 ("Documentation: platform: Delete x86-laptop-drivers.txt")
removed the x86-laptop-drivers.txt file, but forgot to update its
Kconfig.

Fixes: 163ede97 ("Documentation: platform: Delete x86-laptop-drivers.txt")
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>