remove cable_phenology from src/shared


cable_phenology is USEd in science/casa-cnp/bgcdriver.F90. I think possibly it is in shared/ because in ESM1.5 it was included to build. When we merged CABLE3 to make ESM1.6 I wrapped it in a #ifndef UM_CBL, along with some POP thing BUT neglected to remove it from shared/. We should rectify this minor oversight