Disable mdx parsing in turbotrace (#3304)
It's not necessary to enable `MDX` parsing in turbotrace, and there was
a parsing error that caused the build to fail when I was trying to
enable turbotrace in `verce/site`:
https://vercel.com/vercel/vercel-site/7pFWUVMWVAv3jC44WD2nBnwrbJpM
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>
