We never delete or change an obs. Instead, an obs is voided and a new one is created. We need to keep track of the obs that was voided. Currently this is done in a hacky way in the EncounterFormController and ObsController by putting some text into the void_reason column.
Instead, we should have an obs.voided_obs that is foreign keyed back to obs.obs_id. The liquibase-update-to-latest will need to get a new changeSet, the Obs pojo will need to be changed, and the EncounterFormController and ObsFormController will need to stop storing/looking for things in the voidReason attribute.