Documentation: Update x86_64/boot-options.txt

Removed obsolte parameters from boot-options.txt.
Verified by grepping around in arch/x86/.

Signed-off-by: Richard Weinberger <richard@nod.at>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>