CaloBCIDAvgAlg: Use BunchCrossingCondAlg
The MC code-path of the CaloBCIDAvgAlg was still based on the public TrigBunchCrossingTool. Migrate to BunchCrossingAlg.
@ssnyder: I chose a different solution than what we discussed earlier today, the LuminosityCondAlg is untouched.
Moreover: Simplify the code a bit.