Revert "kvserver: disable assertion 'finished proposal inserted'"

Reverts cockroachdb#97606.

This reverts commit f95866d.

pkg/kv/kvserver/replica_proposal_buf.go

@@ -1189,10 +1189,7 @@ func (rp *replicaProposer) registerProposalLocked(p *ProposalData) {
 	if p.createdAtTicks == 0 {
 		p.createdAtTicks = rp.mu.ticks
 	}
-	// TODO(tbg): this assertion fires. Figure out why. See:
-	// https://github.com/cockroachdb/cockroach/issues/97605
-	const enableAssertion = false
-	if enableAssertion && buildutil.CrdbTestBuild && (p.ec.repl == nil || p.ec.g == nil) {
+	if buildutil.CrdbTestBuild && (p.ec.repl == nil || p.ec.g == nil) {
 		log.Fatalf(rp.store.AnnotateCtx(context.Background()), "finished proposal inserted into map: %+v", p)
 	}
 	if prev := rp.mu.proposals[p.idKey]; prev != nil && prev != p {