fix: remove duplicate sitemap route

- app/sitemap.ts already generates the sitemap index via generateSitemaps()
- app/sitemap.xml/route.ts was a duplicate manual version at the same path

app/sitemap.xml/route.ts

@@ -1,27 +0,0 @@
-import { generateSitemaps } from "@/app/sitemap"
-import { getBaseUrl } from "@/lib/sitemap-utils"
-
-export const revalidate = 3600
-
-export async function GET() {
-  const baseUrl = getBaseUrl()
-  const sitemaps = await generateSitemaps()
-
-  const entries = sitemaps
-    .map(({ id }) => `  <sitemap>\n    <loc>${baseUrl}/sitemap/${id}.xml</loc>\n  </sitemap>`)
-    .join("\n")
-
-  const xml = [
-    `<?xml version="1.0" encoding="UTF-8"?>`,
-    `<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">`,
-    entries,
-    `</sitemapindex>`,
-  ].join("\n")
-
-  return new Response(xml, {
-    headers: {
-      "Content-Type": "application/xml",
-      "Cache-Control": "public, max-age=3600, s-maxage=3600, stale-while-revalidate=86400",
-    },
-  })
-}