Remove `fake` methods from model factories

This updates model factories to not support both the instance and
fake methods. Instead, they will only support the instance and
instance stack methods and will take a record class. The record
class can either be a real or fake record. This should help with
a number of other MR factory issues but is also less confusing
when working with model factories, record factories and read
model factories. This makes all of their interfaces consistent.