Removed extra <changefreq> in sitemap xml (#21608)

There should only be one <changefreq> within the sitemap XML as per the [protocol](https://www.sitemaps.org/protocol.html).

apps/docs/internals/generate-sitemap.mjs

@@ -45,7 +45,6 @@ async function generate() {
               <url>
                   <loc>${`https://supabase.com/docs/${path}`}</loc>
                   <changefreq>weekly</changefreq>
-                  <changefreq>0.5</changefreq>
               </url>
             `
           })