[native] Avoid invariant crash in getDevNodeServerURL

Summary:
D6269 updated release builds to hit getDevNodeServerURL, which is causing a crash. This is happening because the result of getDevNodeServerURL is included in the default list of server options in the Developer tools section of the app.

There's probably no risk to calling this in production, especially since we already call dev-hostname.js code from release builds in natNodeServer. It's better to improve readability of the code and remove this invariant than to sidestep it.

Test Plan: Confirm release build no longer crashes

Reviewers: bartek

Reviewed By: bartek

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D6332