cli, puppet, langpuppet: Remove puppet GAPI's

I'm currently refactoring the CLI code. Unfortunately this means a
pretty big churn in the various GAPI frontends. Since nobody is actively
using the puppet frontend code, I'm removing it for now. If someone is
actively using it, and wants to either port it to the new API, or
sponsor the porting of it to the new API, I'm happy to allow it back in.

Sorry Felix, it was a fun idea, and I loved seeing it work, but I can't
personally afford the maintenance cost of having this in right now.

cli/cli.go

@@ -28,8 +28,6 @@ import (
 	cliUtil "github.com/purpleidea/mgmt/cli/util"
 	"github.com/purpleidea/mgmt/gapi"
 	_ "github.com/purpleidea/mgmt/lang" // import so the GAPI registers
-	_ "github.com/purpleidea/mgmt/langpuppet"
-	_ "github.com/purpleidea/mgmt/puppet"
 	_ "github.com/purpleidea/mgmt/yamlgraph"
 
 	"github.com/urfave/cli/v2"