Update language support docs

[timup]

This commit updates docs language to reflect the change in #4528 that removes the inferred default parser.

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory)
• I’ve read the contributing guidelines.

[lydell]

Hmm, actually, does this file provide any useful information at all? I'd say we remove it.

[timup]

Not especially, as the same information is available in /docs/options.md

[j-f1]

Should we keep the part about the Flow test suite somewhere?

[lydell]

No, I don't think so. It was important when Prettier was new an untested, but not so much anymore. It's not even entirely true anymore (Prettier supports all Flow features, but tests/flow does not contain the entire Flow test suite anymore).

[lipis]

So shall we remove it or what?

[lipis]

I say we kill it with fire!

[duailibe]

@timup Do you want to update the PR removing the file?

[j-f1]

IMO the facts that we require a minimum TS version and support all JS proposed features should be kept somewhere.

[duailibe]

Thank you @timup!