Use set-version for nightly publishes (facebook#42903)

Summary:

Changelog: [Internal] - Update publish-npm to use `set-version` for nightly builds

Now that `set-version` basically does what `set-rn-version` does, this diff uses this logic for nightlies only (as dry-run/pre-alpha variants are non-functional right now)

This does not change the flow of build-type `'release'` -- that will still use `set-rn-version` via CircleCI ([job](https://fburl.com/code/6xo3ijwg), [script](https://fburl.com/code/bo8np0tb))  We will eventually replace that too but that will be later.

This allows us to delete `get-and-update-packages.js` which was a helper written specifically for updating monorepo packages for nightlies.

The purpose of this is to eventually conform all version updates to use `set-version` in all types of releases (nightlies, stable)

Reviewed By: cipolleschi

Differential Revision: D53487874