chore: remove condition for node 12 support

refs vitejs#5248

playground/ssr-deps/read-file-content/index.js

@@ -1,9 +1,6 @@
 const path = require('node:path')
 
 module.exports = async function readFileContent(filePath) {
-  const fs =
-    process.versions.node.split('.')[0] >= '14'
-      ? require('node:fs/promises')
-      : require('node:fs').promises
+  const fs = require('node:fs/promises')
   return await fs.readFile(path.resolve(filePath), 'utf-8')
 }