Remove DemographicsTemplates

[ckirkman-IDM]

This is additionally blocked by emodpy-malaria 2.0ification:

EMOD-Hub/emodpy-malaria#87

[kfrey-idm]

Please retain _computeAgeDis() somewhere (doesn't have to be in DemographicsTemplates, just keep it somewhere).

https://github.com/InstituteforDiseaseModeling/emod-api-old/issues/776