MCOL-5044 This patch simplifies addJob interfaces removing extra bool that control mutex locking,

adds additional nullptr dereference check in removeJobs and fixes FairThreadPool
hashmap iter invalidation issues

utils/threadpool/fair_threadpool.h

@@ -39,6 +39,7 @@
 
 namespace threadpool
 {
+
 // The idea of this thread pool is to run morsel jobs(primitive job) is to equaly distribute CPU time
 // b/w multiple parallel queries(thread maps morsel to query using txnId). Query(txnId) has its weight
 // stored in PriorityQueue that thread increases before run another morsel for the query. When query is
@@ -144,7 +145,6 @@ class FairThreadPool
   explicit FairThreadPool(const FairThreadPool&);
   FairThreadPool& operator=(const FairThreadPool&);
 
-  void addJob_(const Job& job, bool useLock = true);
   void threadFcn(const PriorityThreadPool::Priority preferredQueue);
   void sendErrorMsg(uint32_t id, uint32_t step, primitiveprocessor::SP_UM_IOSOCK sock);