fix(wpt): remove stale fixtures before pulling fresh ones (#679)

Fixes: #678

Author: panva

lib/file.js

@@ -37,3 +37,7 @@ export function readJson(file) {
   }
   return {};
 };
+
+export function removeDirectory(directory) {
+  return fs.promises.rm(directory, { recursive: true, force: true });
+}

lib/wpt/index.js

@@ -3,7 +3,9 @@ import path from 'node:path';
 import _ from 'lodash';
 
 import GitHubTree from '../github/tree.js';
-import { writeFile, readJson, writeJson, readFile } from '../file.js';
+import {
+  writeFile, readJson, writeJson, readFile, removeDirectory
+} from '../file.js';
 import {
   shortSha
 } from '../utils.js';
@@ -73,6 +75,9 @@ export class WPTUpdater {
       assets = await this.getAssetList();
     }
 
+    this.cli.startSpinner('Removing stale assets...');
+    await removeDirectory(this.fixtures(this.path));
+
     this.cli.startSpinner('Pulling assets...');
     await Promise.all(assets.map(
       (asset) => this.pullTextFile(fixtures, asset.name)