chore: remove repro_3591.py from PR branch

The reproduction script was added only as evidence for the parser bug.
It does not belong in the committed source tree (the maintainers import
via Copybara) and it broke CI: mypy flagged 12 type errors and the
pyink linter rejected its 4-space indentation. Removing it leaves the
PR as a single, focused type-annotation fix in cleanup_unused_files.py,
which is fully covered by existing unit tests. Repro output is provided
in the PR thread instead.

Author: syzayd