[a11y] Remove space/enter onKeyDown handling for open/close keyboard shortcuts panel

[cshaver]

Summary

This is to fix an issue where trying to close the keyboard shortcuts panel with the Space and Enter keys doesn't work in Firefox or IE. Pressing space opens and closes the panel immediately and pressing enter seems to do nothing.

As far as I can tell it looks like the onKeyDown event is handled on the close button, but then because the focus is set to the "?" button that opens the panel, the corresponding onKeyUp event triggers an onClick and re-opens the panel.

So – I've removed the Enter and Spacebar handling from the close button's onKeyUp handler, which should just allow onClick to do its thing. Similarly, I removed the onKeyDown handler on the open button (if there's more context on disabling the enter key for that button let me know, but that seemed weird to me).

Gifs

Using keycastr to display keystrokes:

• ␣ = Space
• ↵ = Enter
• ⎋ = Esc

Before

After

Reviewers 🙏

@majapw @backwardok

[coveralls]

Coverage increased (+0.02%) to 85.071% when pulling ca4b67c on cshaver:crit--keyboard-close-shortcuts-panel into e76e308 on airbnb:master.

[majapw]

Seems legit! Thanks for the fix. :)