test: unlink symlink in ng add base E2E test

Instead of attempting to delete all files within the directory, the created
symlink can instead be removed on its own. This should prevent odd Windows
failures in CI.

(cherry picked from commit f05b053)

Author: clydin

tests/legacy-cli/e2e/tests/commands/add/base.ts

@@ -1,5 +1,5 @@
 import { assetDir } from '../../../utils/assets';
-import { expectFileToExist, rimraf, symlinkFile } from '../../../utils/fs';
+import { deleteFile, expectFileToExist, symlinkFile } from '../../../utils/fs';
 import { ng } from '../../../utils/process';
 import { expectToFail } from '../../../utils/utils';
 
@@ -15,5 +15,5 @@ export default async function () {
   await expectToFail(() => ng('add', 'add-collection')); // File already exists.
 
   // Cleanup the package
-  await rimraf('node_modules/add-collection');
+  await deleteFile('node_modules/add-collection');
 }