test: ensure add material test has clean material package (#13548)

Author: clydin

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

@@ -1,8 +1,11 @@
-import { expectFileToMatch } from '../../../utils/fs';
+import { expectFileToMatch, rimraf } from '../../../utils/fs';
 import { ng } from '../../../utils/process';
 
 
 export default async function () {
+  // forcibly remove in case another test doesn't clean itself up
+  await rimraf('node_modules/@angular/material');
+
   await ng('add', '@angular/material');
   await expectFileToMatch('package.json', /@angular\/material/);
 }