Remove realpathCache argument in fs.realpath

[winstliu]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

Node 6 removed the cache argument from fs.realpath as it switched to a much faster native implementation. See nodejs/node#3594 for details. As Atom is now on Node 8, this argument is currently sitting there doing...nothing.

Alternate Designs

None.

Benefits

Removal of a confusing argument from a bygone era.

Possible Drawbacks

None.

Applicable Issues

None, though I caught this when working on #1232.

[Arcanemagus]

Would it be clearer to simply omit the options object?

[winstliu]

Yes, it would 😀. Mind was on autopilot there.