fix(@angular-devkit/build-angular): don't set watchOptions in webpack-middleware

`webpack-dev-middleware` doesn't have a `watchOptions`

See: https://github.com/webpack/webpack-dev-middleware/blob/master/src/options.json

Author: alan-agius4

packages/angular_devkit/build_angular/src/webpack/plugins/karma.ts

@@ -120,7 +120,6 @@ const init: any = (config: any, emitter: any, customFileHandlers: any) => {
     // Hide webpack output because its noisy.
     logLevel: 'error',
     stats: false,
-    watchOptions: { poll: options.poll },
     publicPath: '/_karma_webpack_/',
   };