MCOL-513 use a single funcor per thread. ThreadPool was doing one at a time anyway, but in a convpluted way that made it easier to add more if wanted. But it was expensive. Cleanup and polish.

dbcon/joblist/tupleunion.cpp

@@ -775,9 +775,7 @@ void TupleUnion::run()
 
 void TupleUnion::join()
 {
-	uint32_t i;
 	mutex::scoped_lock lk(jlLock);
-	Uniquer_t::iterator it;
 
 	if (joinRan)
 		return;