windows: use go generate to build zsyscall_windows.go

Also remove some empty source files while we are at it.

Change-Id: Ia3a35b274a0428196aee63ee2daacc533285d0ea
Reviewed-on: https://go-review.googlesource.com/2530
Reviewed-by: Rob Pike <r@golang.org>

windows/syscall_windows.go

@@ -14,6 +14,8 @@ import (
 	"unsafe"
 )
 
+//go:generate go run $GOROOT/src/syscall/mksyscall_windows.go -output zsyscall_windows.go syscall_windows.go security_windows.go
+
 type Handle uintptr
 
 const InvalidHandle = ^Handle(0)