[CLEANUP beta] Remove deprecated CP semantics

[cibernox]

I can't tell how long I've been waiting for this moment.

[stefanpenner]

yay

[stefanpenner]

kicking sauce labs

[cibernox]

As a side note, a backwards compatible change is that the setter function always receives the oldValue as 3rd argument.
Formerly it used to check the arity of the setter function to invoke it with or without the 3rd argument. I cannot think on a single good reason to do that now.

[stefanpenner]

@krisselden / @mmun can you review? I flew a red-eye last night, my judgement is likely not the best right now 😴 :

[rwjblue]

Let's prefix with [CLEANUP beta](seems better than nothing and will make changelog work easier).