refactor(@schematics/angular): remove duplicate prompt definition.

This definition is a duplicate of the one already present in the application schematic

Author: alan-agius4

packages/schematics/angular/ng-new/schema.json

@@ -141,9 +141,7 @@
     },
     "zoneless": {
       "description": "Create an initial application that does not utilize `zone.js`.",
-      "x-prompt": "Do you want to create a 'zoneless' application without zone.js (Developer Preview)?",
-      "type": "boolean",
-      "default": false
+      "type": "boolean"
     }
   },
   "required": ["name", "version"]