[core] Issue with robot/model, you can't remove the added frames with removeFrames

[mwulfman]

It appears the safeguard part of the code in Model::removeFrames do the opposite of what it is supposed to do.

If not specifying the frame type, the frames you add using addFrame have the default type OP_FRAME. But then, when you tried removing those frames, without specifying filter argument, it takes by default OP_FRAME, meaning you can't remove the OP_FRAME.
The python api only exposes the add_frame and remove_frames without being able to specify the type or filter argument for the respective function. As a result, the added framed can't be removed.

This looks like a typo as we should be able to remove the OP_FRAME.