chore: remove old imagegen LLMs models (#14597)

These models are implemented in the x/mlxrunner instead.

cmd/cmd.go

@@ -606,17 +606,6 @@ func RunHandler(cmd *cobra.Command, args []string) error {
 	}
 	opts.WordWrap = !nowrap
 
-	useImagegen := false
-	if cmd.Flags().Lookup("imagegen") != nil {
-		useImagegen, err = cmd.Flags().GetBool("imagegen")
-		if err != nil {
-			return err
-		}
-	}
-	if useImagegen {
-		opts.Options["use_imagegen_runner"] = true
-	}
-
 	// Fill out the rest of the options based on information about the
 	// model.
 	client, err := api.ClientFromEnvironment()