Remove/replace uses of fs-extra

[lindsaylevine]

per: #280 (comment)

[ascorbic]

I don't think we should remove it. There are lots of useful functions in there. We should just stick to a compatible version until we drop Node 10 support (which we should do when Next does)

[lindsaylevine]

that's fine w me! let's close this then and leave the renovate PR open til node 10 support is dropped?

[erezrokah]

@lindsaylevine you can close the PR to tell renovate to ignore that specific update.
When you're ready to merge it you can re-request it via #121.

Keeping it open also works