ensure pkg/util/mount compiles & crosses

- move compile time check from linux code to generic code

pkg/util/mount/mount_linux.go

@@ -54,8 +54,6 @@ const (
 // kubelet is running in the host's root mount namespace.
 type Mounter struct{}
 
-var _ = Interface(&Mounter{})
-
 // Mount mounts source to target as fstype with given options. 'source' and 'fstype' must
 // be an emtpy string in case it's not required, e.g. for remount, or for auto filesystem
 // type, where kernel handles fs type for you. The mount 'options' is a list of options,