fix(@schematics/angular): only show legacy browsers deprecation warning when option is used

This ensures that the deprecate warning is only displayed when the option is used.

Author: alan-agius4

packages/schematics/angular/ng-new/index.ts

@@ -63,7 +63,7 @@ export default function(options: NgNewOptions): Rule {
     skipInstall: true,
     strict: options.strict,
     minimal: options.minimal,
-    legacyBrowsers: options.legacyBrowsers,
+    legacyBrowsers: options.legacyBrowsers || undefined,
   };
 
   return chain([