Removed GroundShakingIntensityModel.forbid_instantiation()
Removed GroundShakingIntensityModel.forbid_instantiation()


Former-commit-id: 52a6e1b6fdf22b226d12b913d6f6f70845f3db05
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine