Add 'clean' script to package.json (#53442)

It removes empty folders from now-removed packages so that test-all will
run without complaining. Also removes folders that are empty except for
`node_modules`.

scripts/remove-empty.js

@@ -0,0 +1,10 @@
+const fs = require('fs')
+const path = require('path')
+for (const d of fs.readdirSync("../types")) {
+  const dir = path.join("../types", d)
+  const files = fs.readdirSync(dir)
+  if (files.length === 0 || files.length === 1) {
+    console.log("Deleting unused directory", dir)
+    fs.rmdirSync(dir, { recursive: true })
+  }
+}