uefi-services: Drop use of unstable alloc_error_handler feature

[nicholasbishop]

As of 2022-12-18, we can rely on the default_alloc_error_handler feature which was stabilized in rust-lang/rust#102318. The behavior of the default handler is to panic, essentially the same as our current custom one.

This needs an MSRV bump, so we can expect to merge this around March 18.

#452

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)