Turbopack: remove pages router double template (#86842)
Webpack does:
`templates/edge-ssr.js -> user's pages/index.js`
Turbopack does
`templates/edge-ssr.js { INNER_PAGE_ENTRY => \"[project]/packages/next/dist/esm/build/templates/pages.js { INNER_PAGE => \\\"[project]/test/tmp/next-test-1764875742357-479/pages/index.js`
`VAR_USERLAND` here: https://github.com/vercel/next.js/blob/ee3d017e43eb953a62746a0e6110a94dc7a3c980/packages/next/src/build/templates/edge-ssr.ts#L12-L13
for Webpack is actually the user's page file with the `export default Page()`
for Turbopack is actually whatever `templates/pages.js` exports and it relies on this default reexport: https://github.com/vercel/next.js/blob/38ef2360e1e133f329a9061ce17aad8aaab33cb2/packages/next/src/build/templates/pages.ts#L15 while ignoring everything else in there
