doc: Remove --allow-64-bit leftover from help text.
doc: Remove --allow-64-bit leftover from help text.

Removes help text left behind when --allow-64-bit was turned into
default behavior + warning.

Signed-off-by: Knut St. Osmundsen <faf3fd3ed24c7f43e965a24b9277814d40cbc1b4@anduin.net>
Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm