Ember 2.4+ does not need the assign polyfill

[NullVoxPopuli]

No description provided.

[twokul]

Related to #819.

[twokul]

I am not sure we want to merge this into 3.0-beta just yet since we would like to drop all the "< Ember 2.4" targets but keep Ember 2.4, for now. I believe, assign appears in Ember proper in 2.5.

[mixonic]

I believe the correct fix here is to use native Object.assign and stop using Ember's API at all. Then we can drop the polyfill. The browser support commitment for ember-table is fuzzy, but we're certainly not supporting IE11 in 3.0 and that was really the blocker on using Object.assign.

https://caniuse.com/mdn-javascript_builtins_object_assign

[mixonic]

The only use of assign in Ember Table is Object.assign. So, I'm really not even sure what this dependency is doing. Certainly on our supported browsers it is doing nothing. Merging this.