pkg/system: remove windows stubs for MkDev/MkNod

They're not used anywhere, so let's remove them; better to have
a compile error than a panic at runtime.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/system/mknod_windows.go

@@ -1,11 +0,0 @@
-package system // import "github.com/docker/docker/pkg/system"
-
-// Mknod is not implemented on Windows.
-func Mknod(path string, mode uint32, dev int) error {
-	return ErrNotSupportedPlatform
-}
-
-// Mkdev is not implemented on Windows.
-func Mkdev(major int64, minor int64) uint32 {
-	panic("Mkdev not implemented on Windows.")
-}