These are unused since CL 153837. illumos64Bit was added by CL 174457
but was never used.

Change-Id: I34a1bd41cf70f8a07e57f93a71de3c6034fcaf7b
Reviewed-on: https://go-review.googlesource.com/c/go/+/175358
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>