Directly require clipboard from Electron

[50Wliu]

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

As far as I can tell the "safe-clipboard" workaround was for an Electron bug that was fixed somewhere around atom-shell 0.24.0. Searching for "clipboard linux" on the electron issues list doesn't yield any crash results and the docs don't have anything Linux-specific, so I think that we should be good now.

Alternate Designs

None.

Why Should This Be In Core?

This cleans up some old code present in core.

Benefits

Requiring the clipboard is more straightforward.

Possible Drawbacks

It is possible that the crash still exists and I'm searching for the wrong thing.

Verification Process

I currently don't have a Linux distribution set up, so I'm unable to verify that using the renderer clipboard does not crash Atom.

Applicable Issues

Refs electron/electron#1372

[maxbrunsfeld]

I just tested this on my Ubuntu VM. Requiring clipboard directly from electron and calling writeText and readText on it worked just fine from the renderer process.

[maxbrunsfeld]

Thanks @50Wliu!