Remove deprecated EmberError and assign

[wozny1989]

Task:

• Remove deprecated EmberError - https://deprecations.emberjs.com/id/deprecate-ember-error
• Remove deprecated assign - https://deprecations.emberjs.com/id/ember-polyfills-deprecate-assign

[dwickern]

@RobbieTheWagner could you make a release with this fix? It's a blocker for ember v5

[RobbieTheWagner]

@dwickern yes, apologies for the delay! I need to update this addon in general and setup release-plan so we can easily do releases in the future.

[dwickern]

Thank you! ember-ajax is archived and ember-fetch removed all of its functionality in version 8. This addon seems like the easiest path forward.

[RobbieTheWagner]

2.0.0 has been released, please let me know how it works for you!

[dwickern]

Works great!

I see now there's an RFC to deprecate ember-fetch. If that happens, maybe this addon could drop the ember-fetch dependency and wire up the test waiters directly.