GeneratorObjectsTPCnv: Fix genconf warnings.

TPCnv libraries declare Gaudi plugin factories for the TP converters. Normally, the TPCnv libraries should not be linked against libraries other than the EventPool libraries. However, it is possible for one TPCnv library to link against another TPCnv library. In that case, genconf may emit warnings that one library's factory is visible from another. Clean up by moving TPCnv factories into their own libraries (linked against the corresponding TPCnv library). For now, do this only for TPCnv libraries which others actually link against and for which we've seen these warnings.