Remove the temporary referenceDescriptor projection from formal/differential.mjs #222

Context

#219 added the deletions counter to the shared Observation record in formal/conformance-observations.qnt. The bidirectional differential compares a candidate branch against its merge-base, and that merge-base (d470b2f) did not declare the field. referenceDescriptor in formal/differential.mjs bridges this by projecting a zero deletions baseline into reference traces whose conformance-observations.qnt lacks the field, and a test covers it including negative controls.

Why this becomes dead code

Once #219 merges, every later PR's merge-base declares deletions, so the bridge never activates again. It only matters for branches whose merge-base predates #219.

Task

• Remove referenceDescriptor and its test from formal/differential.mjs once no supported reference revision lacks the field.
• Pass the plain descriptor to both loadHistories calls and to the reverse prepareReplay.
• Run make differential on the PR to confirm the shards still agree.

Related

• Add explicit cache get, put, and exact-key delete APIs #217 (direct-ops parent): for the later put slice, prefer a profile-local observation channel instead of widening the shared record, so the smoke traces and witness fixtures do not churn again and no second bridge is needed.