Remove enableUserSelectHack, set to false by default

[neaumusic]

Rant: We had an incredibly difficult time connecting the dots between a setState causing a modal to hide and figuring out why the user was losing focus in Gmail. I've probably spent 10+ hours digging through our codebase since we have a ton of places where we manage the user's selection. The last thing I expected was for the Draggable wrapper on that modal to be removing all ranges from the document. I had to resort to a binary search "comment half of everything out, see if it still works, repeat" which was still extremely difficult because I didn't consider the very last element to be the one causing issues.

Repro: The user selects text in any Gmail compose window, opens formatting, clicks bold, our modal disappears (from something like document.addEventListener('mousedown', checkIsOutsideAndHideModal), and the user loses their selection and bold is not applied

RCA: https://github.com/react-grid-layout/react-draggable/blob/master/lib/DraggableCore.js#L97 This comment explains why it exists, but the code that consumes this flag is mostly about removing document ranges https://github.com/react-grid-layout/react-draggable/blob/master/lib/utils/domFns.js#L168