libpod: remove shutdown.Unregister()

It is never used and needed so let's just remove some dead code.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/shutdown/handler.go

@@ -140,29 +140,3 @@ func Register(name string, handler func(os.Signal) error) error {
 
 	return nil
 }
-
-// Unregister un-registers a given shutdown handler.
-func Unregister(name string) error {
-	handlerLock.Lock()
-	defer handlerLock.Unlock()
-
-	if handlers == nil {
-		return nil
-	}
-
-	if _, ok := handlers[name]; !ok {
-		return nil
-	}
-
-	delete(handlers, name)
-
-	newOrder := []string{}
-	for _, checkName := range handlerOrder {
-		if checkName != name {
-			newOrder = append(newOrder, checkName)
-		}
-	}
-	handlerOrder = newOrder
-
-	return nil
-}