We already removed it from the online docs with #35132.
Currently it can only be "Built-In Types" (Variant types) or "Core"
(everything else), which is of limited use.
We might also want to consider dropping it from `ClassDB` altogether
in Godot 4.0.
See https://github.com/godotengine/godot/pull/23658#issuecomment-562706669
The method was implemented back when Dictionary.get(key, default) did not
exist, but now that it does we do not need a custom method in CharFXTransform.
It's a new feature in 3.2, so does not break compat with 3.1.x.
