fix: "Cannot access uninitialized variable" in Safari when using "$env/dynamic/public"

[bfanger]

Fixes #11364

Using global await is causing issues in Safari: https://bugs.webkit.org/show_bug.cgi?id=242740.
This bug was introduced in 9439190

This PR removes a fallback, but I'm not sure when the global variable is available but the env property is null or undefined.
So this PR might re-introduce a bug, but that is probably less common bug than trying to use "$env/dynamic/public" on sites that need to support iOS.

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[bfanger]

Diving deeper into the change I see the env: ${!client.uses_env_dynamic_public || state.prerendering ? null : s(public_env)}

Closing the PR as it would break prerenderd pages and a quick fix is not obvoius.
( It's hard to synchronously & conditionally import the environment variables without using global await )

Work in progress bfanger/kit: fix/sveltekit-v2-safari