Remove --version spawn from debugger shell preparation (#56706)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56706

Addresses an issue where on macOS, we briefly flashed the RNDT app icon in the Dock. (This has been raised to us recently by Expo.)

**More info**

The `unstable_prepareDebuggerShell` health check was spawning the Electron binary with `--version` after a successful `dotslash fetch`. Invoking the native binary causes the app icon flash.

- I couldn't find an Electron-side way to eliminate this (e.g. headless).
- DotSlash already performs mandatory verification of every fetched artifact. The additional `--version` spawn was therefore redundant/overkill.

Changelog:
[General][Fixed] - React Native DevTools will no longer briefly flash in the system dock/taskbar when starting Metro

Reviewed By: cortinico

Differential Revision: D104061238

fbshipit-source-id: 5baafbc9a452438bb6ddcfb584975cae12618e0c