Fix calculation of gamma

Change speed of light to 1.
Momentum and mass are given in GeV, therefore speed of light does not need to be c=3e8.

sim/detectors/trd/CbmTrdDigitizer.cxx

@@ -204,7 +204,7 @@ void CbmTrdDigitizer::Exec(Option_t*)
     else
       mod = imod->second;
     mod->SetLinkId(fCurrentInput, fCurrentMCEntry, iPoint);
-    Double_t gamma = TMath::Sqrt(1 + TMath::Power(track->GetP() / (3.e8 * track->GetMass()), 2));
+    Double_t gamma = TMath::Sqrt(1 + TMath::Power(track->GetP() / (track->GetMass()), 2));
     mod->SetGamma(gamma);
     mod->MakeDigi(point, fCurrentEventTime, TMath::Abs(track->GetPdgCode()) == 11);
   }