Rollup merge of #104459 - notriddle:notriddle/main-js-iife, r=GuillaumeGomez

rustdoc: remove unused JS IIFE from main.js

This [IIFE] made sense when it was added in f0683f98fa114cc4f9e795031f44be3eebb65790 and there was a local variable scoped to it, but now it only sets two globals, so it does nothing.

[IIFE]: https://developer.mozilla.org/en-US/docs/Glossary/IIFE "immediately invoked function expression"

Author: matthiaskrgr