cmd/headscale/cli: remove legacy namespace and machine aliases

The --namespace flag on nodes list/register and debug create-node was
never wired to the --user flag, so its value was silently ignored.
Remove it along with the deprecateNamespaceMessage constant.

Also remove the namespace/ns command aliases on users and
machine/machines aliases on nodes, which have been deprecated since
the naming changes in 0.23.0.

cmd/headscale/cli/root.go

@@ -14,10 +14,6 @@ import (
 	"github.com/tcnksm/go-latest"
 )
 
-const (
-	deprecateNamespaceMessage = "use --user"
-)
-
 var cfgFile string = ""
 
 func init() {