Add the API call that will eventually delete the data for a particular user
Add a basic test to see if the user events themselves disappear
Also need to test that query data is removed when deleting users
Uningest the events when a deletion request arrives
Need a method to delete the user event store...
Add an API to delete a list of keys generated by an enumerator
Add a test for the new API call
Implement key deletion for the memory store
Tests for behaviour when keys are missing from the source and for different sets of keys