Remove references to AdapterFetch

[patocallaghan]

Part of #444

Fixes deprecate-fetch-ember-data-support deprecations

[patocallaghan]

All DRFSerializer (Django Rest Adapter) tests are currently failing 🔴

[Techn1x]

Seems the specific tests that are failing are DRF tests that are checking the error payload - any test that has the line reason.errors[0] has an issue (errors is not defined), eg

ember-data-factory-guy/tests/unit/shared-adapter-behaviour.js

Line 81 in 1d6cd99

assert.equal(reason.errors[0].status, '404');

It's failing to generate the correct error payloads, instead it's throwing an actual error in the django adapter - traced it back to this line

https://github.com/dustinfarris/ember-django-adapter/blob/32035bb13d57cb8896bdf1eda560d027e76b6760/addon/adapters/drf.js#LL108C4-L108C60

with fetch adapter: payload = "Not Found"
without fetch adapter: payload = null

It seems the FetchAdapter parses the fetch response for errors slightly different than the RestAdapter that the DjangoAdapter uses

From there I get a bit out of my depth, but I hope that helps you out