fix(@angular/cli): ng update remove duplicate dryRun in help

Closes #12423

Author: alan-agius4

packages/angular/cli/commands/update-impl.ts

@@ -54,7 +54,7 @@ export class UpdateCommand extends SchematicCommand<UpdateCommandSchema> {
       collectionName: this.collectionName,
       schematicName: this.schematicName,
       schematicOptions: options['--'],
-      dryRun: options.dryRun,
+      dryRun: !!options.dryRun,
       force: false,
       showNothingDone: false,
     });

packages/angular/cli/commands/update.json

@@ -22,14 +22,6 @@
           "$default": {
             "$source": "argv"
           }
-        },
-        "dryRun": {
-          "type": "boolean",
-          "default": false,
-          "aliases": [
-            "d"
-          ],
-          "description": "Run through without making any changes."
         }
       },
       "required": [