validation: make CCheckQueueControl's CCheckQueue non-optional

This simplifies the construction logic and will allow the constructor and
destructor to lock and unlock uncondiationally.

src/bench/checkqueue.cpp

@@ -56,7 +56,7 @@ static void CCheckQueueSpeedPrevectorJob(benchmark::Bench& bench)
 
     bench.minEpochIterations(10).batch(BATCH_SIZE * BATCHES).unit("job").run([&] {
         // Make insecure_rand here so that each iteration is identical.
-        CCheckQueueControl<PrevectorJob> control(&queue);
+        CCheckQueueControl<PrevectorJob> control(queue);
         for (auto vChecks : vBatches) {
             control.Add(std::move(vChecks));
         }