Control HCRawBankDecoder warning print-out (@johndan)

Use Warning() instead of warning() << to control the number of times HCRawBankDecoder complains about duplicated cell ID in the (rare) event that data are corrupted and Herschel cellID information is scrambled - as seen in 3 specific runs in 2017 (see thread on lhcb-davinci "Duplicated Cell ID warnings...") when the detector was known (elog) to be in an ill-defined state.

Cherry-picked from !2831 (merged)