Fixture Adapter still mutates FIXTURES arrays on create/update/deleteRecord

[fivetanley]

This can lead to many gotchas while testing. As @bmac suggested we should probably have the Fixture Adapter account for this and manage state, and make some initializer that resets using the original array.

[stefanpenner]

Or have he fixture adapter do a stringify and parse. Or some other structured clone

[wecc]

The FixtureAdapter has been deprecated (#3091) and is no longer included in Ember Data by default.

The code for FixtureAdapter has been moved to emberjs/ember-data-fixture-adapter, please re-open in that repo if this is still an issue.