fix(@angular/cli): hide private schematics from ng g help output

With this change we don't display private schematic in `ng generate` help output.

Author: alan-agius4

packages/angular/cli/src/commands/generate/cli.ts

@@ -67,6 +67,10 @@ export class GenerateCommandModule
     }
 
     for (const schematicName of schematicNames) {
+      if (schematicsInCollection[schematicName].private) {
+        continue;
+      }
+
       const {
         description: {
           schemaJson,