Revert recent changes to dead code analysis (this time, stable)

[compiler-errors]

Hi -- I'd also like to backport the relevant changes from #128606 onto stable if possible, given that it's likely we're making a point release.

I'll open a zulip thread on T-release: #128618 for 1.80.1.

This would fix #128617, which is a 1.79->1.80 regression.

[rustbot]

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  LD_LIBRARY_PATH: /opt/hostedtoolcache/Python/3.12.4/x64/lib
##[endgroup]
fatal: unknown commit origin/master
fatal: unknown commit origin/beta
All commits in `HEAD` are present in `master`
All commits in `HEAD` are present in `beta`
src/ci/scripts/verify-stable-version-number.sh
shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}

[pietroalbini]

Included in #128635.