Remove setImmediate polyfill (#27567)

src/vector/index.ts

@@ -25,9 +25,6 @@ import { extractErrorMessageFromError } from "matrix-react-sdk/src/components/vi
 import { parseQsFromFragment } from "./url_utils";
 import "./modernizr";
 
-// Make setImmediate available in bundle
-import "setimmediate";
-
 // Require common CSS here; this will make webpack process it into bundle.css.
 // Our own CSS (which is themed) is imported via separate webpack entry points
 // in webpack.config.js