doc: remove redundant parameter comments from fs

[firedfox]

Pull Request check-list

• Does make -j8 test (UNIX) or vcbuild test nosign (Windows) pass with
  this change (including linting)?
• Is the commit message formatted according to CONTRIBUTING.md?
• If this change fixes a bug (or a performance problem), is a regression
  test (or a benchmark) included?
• Is a documentation update included (if this change modifies
  existing APIs, or introduces new ones)?

Affected core subsystem(s)

• doc

Description of change

Some old version parameter comments are left in the fs doc. Such as following path and callback at last:

## fs.readdir(path[, options], callback)

* `path` {String | Buffer}
* `options` {String | Object}
  * `encoding` {String} default = `'utf8'`
* `callback` {Function}

* `path` {String}
* `callback` {Function}

This change removes them.

See commit 060e5f0 and #5943 for reference.

[mscdex]

LGTM

[cjihrig]

LGTM

[eljefedelrodeodeljefe]

LGTM

[silverwind]

LGTM, landed in 4039ef1.

[silverwind]

Not applicable for LTS because 060e5f0 that introduced the issue is a semver-major.

[MylesBorins]

@silverwind in future if PR's are not applicable can you add the dont-land-on-v4.x label

Thanks for the hard work!!!

[jasnell]

Quite odd. Glad this was caught. Thank you!

[MylesBorins]

as far as I can tell it would seem like these changes are only applicable to master