Clean up ICaloElectron

We currently have two very similar interfaces, https://gitlab.cern.ch/lhcb/LHCb/-/blob/master/CaloFuture/include/CaloFutureUtils/ICaloElectron.h and https://gitlab.cern.ch/lhcb/LHCb/-/blob/master/CaloFuture/include/CaloFutureInterfaces/ICaloFutureElectron.h The first ones does not have an actual implementation or at least I cannot find it. Calo reconstruction algorithms use the latter.

This MR removes the ICaloElectron interface. The only place where it is still used are some Falvour Tagging algorithms, namely:

• https://gitlab.cern.ch/lhcb/Rec/-/blob/master/Phys/FlavourTagging/src/Features/FeatureGenerator.h
• https://gitlab.cern.ch/lhcb/Rec/-/blob/master/Phys/FlavourTagging/src/Taggers/OSElectron/TaggerElectronTool.h

The corresponding cpp files set the tool to "CaloElectron" but such a tool does not exist as far as I can see. Is this actually being used or working at all @cprouve @bkhanji ? Could the Flavour Algorithms use ICaloFutureElectron instead?