Two MC-specific conditions still remained in FittedHit

[raffaelladevita]

1. the hit uncertainty is defined differently for data/mc;
2. the time walk is not applied to mc.

The check is done here on the presence of the MC::Particle bank, which is compatible with using real run numbers. Further evaluation is needed to decide whether these can be removed

Originally posted by @raffaelladevita in #434 (comment)