Refs #30213 -- Removed post-startup check for Watchman availability.

[carltongibson]

This is checked at startup in get_reloader(). The runtime check ties the implementation to Watchman excessively.

Hey @orf 👋 — can I ask for your thoughts here? I was looking at ticket-30213, and this double-check seems a bit excessive… 

• Is it likely Watchman is available at startup but then becomes unavailable? (get_reloader() already checked it was available... 🤔)
• Is that worth privileging in relation to other reloader strategies?
• Can we remove this check?

Sorry if this is re-treading old ground.

Thanks! 🎁