Minor thread-safety improvements to HLTrigger/HLTcore

-Converted a static to const to avoid complaints from static analyzer.
-Removed use of HLTConfigCounter since wasn't thread safe and wasn't
 actually doing anything useful.
Merge pull request #4747 from Dr15Jones/threadSafetyImprovementsForHLTriggerHLTcore

HLTrigger/HLTcore -- Minor thread-safety improvements