This reverts commit 1b739671
(https://go-review.googlesource.com/c/sys/+/133015)

Reason for revert: breaks the build. No Syscall9 on linux/arm.
Not obvious this was ever compiled, much less tested. (Unless it
was only for gccgo, but that was never specified.)

Fixes golang/go#27475

Change-Id: I5ed04c9ab672ce33adc64bdaec601bf73df42269
Reviewed-on: https://go-review.googlesource.com/133095Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>