Turbopack: remove unused transforms (#83567)
- `next_shared/transforms/next_shake_exports.rs`: dead code
- `turbopack-ecmascript-plugins/src/transform/modularize_imports.rs`: dead code
- `next_shared/transforms/next_page_config.rs`: amp, unsupported anyway
- `next_shared/transforms/next_amp_attributes.rs`: amp, unsupported anyway
See also https://nextjs.org/blog/next-15-5#amp-support
