Fix memory leaks in jet reconstruction

This fixes a few memory leaks in jet reconstruction:

• ATLASRECTS-5790: A histogram in the JVT tool which is allocated by a call to TDirectoryFile::Get(...) but never deleted
• ATLASRECTS-5681: A subtle double-copy of an IConstituentExtractor in ExtractorRange::bump(...) where clone() was being called once in the function and again in the implicit copy-constructor used in the return statement.
• Some histograms being grabbed from ROOT files and not deleted in jet calibration tools.

I've also cleaned up the destructor for JMSCorrection for simplicity while I was checking these.