Update the syscall numbers and error constants on macOS 10.13 with iOS
SDK 11.1.

The removed syscalls are all removed or marked as deprecated/old in the
following list

  https://opensource.apple.com/source/xnu/xnu-4570.1.46/bsd/kern/syscalls.master

which according to

  https://opensource.apple.com/release/macos-1013.html

is the kernel version used for macOS 10.13.

The poll function was moved around because I missed to regenerate the
zsyscall_darwin_*.go files in CL 74290.

Change-Id: I747c8c842f78f3db8d25b46759265aa99da9d739
Reviewed-on: https://go-review.googlesource.com/75972
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>