* feat: removing djangoapp `demographics`, step 1
This step removes the models, the references to the models, and adds a
migration to drop both tables (`HistoricalUserDemographics` didn't
have a corresponding model but was still a valid table).
Once this has deployed, this will be removed from `INSTALLED_APPS` and
completely removed.
No other apps in the repository currently reference this djangoapp in
code or tables.
FIXES: APER-3560
12569b459f