Disable DAB

See issue: https://github.com/kubernetes-incubator/kompose/issues/390

Disable DAB as it is hard to maintain / not much usage / DAB is still
experimental in Docker and there hasn't been much movement:
https://github.com/moby/moby/issues/26876

MarkDeprecated does not work at the moment due to issue:
https://github.com/kubernetes-incubator/kompose/issues/652

However, that is not a blocker as we `fatalF` within `ValidateFlags`

pkg/app/app.go

@@ -118,6 +118,7 @@ func ValidateFlags(bundle string, args []string, cmd *cobra.Command, opt *kobjec
 
 	if len(bundle) > 0 {
 		inputFormat = "bundle"
+		log.Fatalf("DAB / bundle (--bundle | -b) is no longer supported. See issue: https://github.com/kubernetes-incubator/kompose/issues/390")
 		opt.InputFiles = []string{bundle}
 	}