cleanup obsolete PhysList and add G4Exp, G4Log to Urban93

Obsolete Physics Lists LHEP, LHEP_EMV, QGSP_BERT_EMLGG, QGSP_BERT_EMLGN, QGSP_BERT_EMLNoDel are removed. 

UrbanMscModel93 was cleaned up: G4Exp and G4Log are used instead of std::log, std::exp, two short methods inlined.

Results should be unchanged only some CPU advantage.