Two real-but-cosmetic dead-code findings from the review-bot corpus (re-adjudicated): scanner.py's dataset dead store; _TEST_FILES_SKIPPED_KEY unused

[gadievron]

Re-adjudication of the #481 corpus (against current master) found two true positives the original sweep had filed as false-positive/stale. Both are non-behavioral no-ops (consequence-triaged; the "no unaddressed behavioral finding" headline stands) — this issue is the cleanup rider:

1. core/scanner.py:907 — dataset = None is the last statement of the outer llm-reachability stage: wrap the post-read stage body so non-LLM failures degrade instead of aborting the scan #268 wave-catch handler; no read of the local follows (the sibling inner handler at :595 IS read at :608 — that one is live; only the outer is dead). Flagged by the review bot on PR fix(scanner): llm-reachability stage body degrades instead of aborting the scan #371.
2. _TEST_FILES_SKIPPED_KEY (defined core/scanner.py:1388) — git grep finds exactly one line in the whole tree: its own definition. Zero readers, and :1392 still duplicates the literal it was meant to replace. Flagged on PR fix(report): pipeline_output.json carries the four coverage fields the CHANGELOG claims, plus the dominant test-file exclusion #405.

Commands: git grep -n _TEST_FILES_SKIPPED_KEY origin/master -- → 1 hit (the definition); token scan of the scanner function shows no dataset read after :907.