Removed use of ConstProductRegistry since the function is deprecated

The code was attempting to lookup a value for a ParameterSet for another module via the ConstProductRegistry.
The particular function being called will be going away for thread safety reasons. The code was changes to
instead use the ProcessHistory at beginRun to lookup the same information. This is actually superior since
the ConstProductRegistry call could have caused an exception if different jobs were using different configurations
for the module being searched.
In addition to the above I removed unused member data, fixed an end of job memory leak and added a
'fillDescriptions' to properly handle the case where a tracked parameter was allowed to not be specified.