deps: add acorn stage-3 plugins

This adds bigint, class-fields, numeric-separators, static-class
features, private class methods and fields as dependency. That way
it's possible to use these in combination with acorn to parse these
language features.

This also removes a couple of files that were not necessary for
Node.js to reduce the code base.

PR-URL: https://github.com/nodejs/node/pull/27400
Refs: https://github.com/nodejs/node/issues/27391
Refs: https://github.com/nodejs/node/issues/25835


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>