Follow-up to #2110 (which generalised pruneStaleKeys to Map<string, T>).
Identified by the simplify reviewer on that PR as the only other
in-tree caller of the same shape: `for (const id of map.keys()) { if
(!liveIds.has(id)) map.delete(id); }`.
Net: -3 lines, one less hand-rolled GC loop. No behaviour change —
the helper does exactly what the inline block did.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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