Fix unmount redeclaration on darwin in github.com/docker/docker/pkg/mount

Signed-off-by: Fabian Kramm <kramm@covexo.com>

pkg/mount/mounter_unsupported.go

@@ -5,7 +5,3 @@ package mount // import "github.com/docker/docker/pkg/mount"
 func mount(device, target, mType string, flag uintptr, data string) error {
 	panic("Not implemented")
 }
-
-func unmount(target string, flag int) error {
-	panic("Not implemented")
-}

pkg/mount/unmount_unsupported.go

@@ -0,0 +1,7 @@
+// +build windows
+
+package mount // import "github.com/docker/docker/pkg/mount"
+
+func unmount(target string, flag int) error {
+	panic("Not implemented")
+}