unix: remove ClockGettime for darwin/amd64 on Go 1.11

This was erroneously introduced by CL 170297

SYS_CLOCK_GETTIME is not defined on darwin.

Fixes golang/go#31203

Change-Id: I39b1f19c4c9d7e9cb67569c4cb2764d64f158c0f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/170299
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/zsyscall_darwin_amd64.1_11.go

@@ -683,16 +683,6 @@ func Chroot(path string) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func ClockGettime(clockid int32, time *Timespec) (err error) {
-	_, _, e1 := Syscall(SYS_CLOCK_GETTIME, uintptr(clockid), uintptr(unsafe.Pointer(time)), 0)
-	if e1 != 0 {
-		err = errnoErr(e1)
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Close(fd int) (err error) {
 	_, _, e1 := Syscall(SYS_CLOSE, uintptr(fd), 0, 0)
 	if e1 != 0 {