CaloRec: Remove StatusCode return from declareConstant.
ToolWithConstantsMixin::declareConstant was returning a StatusCode. However, this is used in constructors, so in practice, the return value was never being checked. Pending changes to Gaudi will start giving warnings about this.
There's no point in returning a StatusCode if it can't reasonably be checked, so just change declareConstant (and add_constant) to be void.
Fixes ATLASRECTS-5355.
Edited by Frank Winklmeier