Eliminate unused or unnecessary ObservableArray methods from ObservableArrayDef

[samreid]

From #330 there are several TODOs related to this. I will point them to this issue. This may be done after migration.

[samreid]

Part of this will be tracked in #279

[samreid]

Many of the occurrences of getArrayCopy are in Energy Forms and Changes, I opened an issue for that.

[samreid]

I'm not planning on working on this in the near future.