Remove experimental fontLoaders option from next.config.js (#46886)
Currently there's an experimental option in `next.config.js` that lets you define default subset(s) to preload for all your fonts. [docs](https://nextjs.org/docs/basic-features/font-optimization#specifying-a-subset)
Over time we haven't seen much use of this option, and we are defining the subsets in the font function call in all our examples/docs. Imo it would be fine to drop this option.
This PR removes that experimental option. If you happen to use it you'll get a build error with [a link](https://github.com/vercel/next.js/blob/f67af163cd625ad7a2d6141edd2b8e2679e14996/errors/google-fonts-missing-subsets.md).
Next step (breaking change for next major) would probably be to remove the preload and subsets properties from `next/font/google` calls, and just have something like [`preloadSubsets“](https://vercel.slack.com/archives/C8EAN8A94/p1674868993169559?thread_ts=1674707555.461809&cid=C8EAN8A94) that is required.