docs: remove $1M challenge banner (apify#3455)

The Apify $1M Challenge has ended, so the announcement bar linking to it
should be removed from the docs site.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: barjin <61918049+barjin@users.noreply.github.com>

Author: Copilot

website/docusaurus.config.js

@@ -273,10 +273,6 @@ module.exports = {
                 hideable: true,
             },
         },
-        announcementBar: {
-            id: `apify-1m-challenge`,
-            content: `<b><a href="https://apify.com/challenge">Apify $1M Challenge 💰</a></b> Earn and win building with Crawlee!`,
-        },
         navbar: {
             hideOnScroll: true,
             title: 'Crawlee',