refactor: move secondary entry point rollup configs.

packages/core/testing/rollup.config.js

@@ -0,0 +1,19 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+export default {
+  entry: '../../../dist/packages-dist/core/testing/index.js',
+  dest: '../../../dist/packages-dist/core/bundles/core-testing.umd.js',
+  format: 'umd',
+  moduleName: 'ng.core.testing',
+  globals: {
+    '@angular/core': 'ng.core',
+    'rxjs/Observable': 'Rx',
+    'rxjs/Subject': 'Rx',
+  }
+};