Remove support for babel-eslint

[sindresorhus]

It's not maintained anymore, so I don't think it makes sense for us to support it.

• Document that babel-eslint is not supported.
• Remove test.babelLegacy().
• Detect and throw at runtime?
• Remove workarounds that are fixed in @babel/eslint-parser, like: https://github.com/sindresorhus/eslint-plugin-unicorn/pull/1036/files#diff-66bd496c5747eb2ce80ffc1d5e923d08c0bc538e37af77e1078e106e992d7a4aR11-R13, and ExperimentalRestProperty node

I think we can do 1 right now, and do the rest a little bit later on to give people time to migrate.

@fisker Thoughts?

[fisker]

In my experience,

1. babel-eslint is still very popular, people don't even know there is a new one.
2. @babel/eslint-parser is hard to config.

I think it's still too early to remove support for babel-eslint.

[sindresorhus]

We should at least document that @babel/eslint-parser is recommended to make people aware.

[fisker]

Sure.

[fisker]

• Document that babel-eslint is not supported.

babel-eslint already have show deprecated message when installing, babel/babel#12702

• Detect and throw at runtime?

I don't think it's necessary.

• Remove workarounds that are fixed in @babel/eslint-parser, like: Refactor: replace isSameNode with hasSameRange #1036 (files), and ExperimentalRestProperty node

ExperimentalRestProperty removed in #1211, but that workaround is still an issue, I'll report to the new babel repo.