nasm: remove unused target package

When nasm was added in da8d09b7, it got both the host and the target
variants even though it doesn't have a Config.in and the target variant isn't
used anywhere. Therefore, this patch removes the unused target variant.

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>