Including linux/stat.h in mkerrors.sh is no longer necessary because the
statx types and constants were added to the glibc headers.

Change-Id: I643c35fd2da76dd2c15015556658d7fa862249c4
Reviewed-on: https://go-review.googlesource.com/129100
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>