fix: don't stash away original history methods so other libs can monkeypatch it

[dummdidumm]

Some other libraries might hook into history.replaceState/pushState to do additional work. This no longer works since the introduction of shallow routing because we're stashing away the original history methods. This PR adjusts the DEV time check logic so that this is no longer necessary.
Fixes #11499
Fixes vercel/analytics#121

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[Rich-Harris]

one small suggestion but otherwise LGTM

[benmccann]

thank you for fixing this!!

[lukasmalkmus]

This PR, released as part of v2.3.4 results in a new warning that wasn't previously there:

[Warning] Avoid using `history.pushState(...)` and `history.replaceState(...)` as these will conflict with SvelteKit's router. Use the `pushState` and `replaceState` imports from `$app/navigation` instead. (client.js, line 2580)

I'm not using history as suggested by the warning. I'm using goto in a couple of places, from $app/navigation. I haven't changed anything. The warning is not present with v2.3.3.

From a quick test, commenting out all the goto calls still resulted in the warning.