ast.Node should support Delete/Unset at any depth, possibly with options to remove empty arrays and objects

[scr-oath]

I'd like to think that, for massive changes to json structures, parsing into, using, then marshaling out of an AST should be more performant than a gjson/sjson pair that has to re-parse newly returned []byte. One convenience feature that is missing is the ability to delete at any depth by path (...any for ast.Node style).