This removes the feature which disables renderborder when selecting a border region larger than the camera while in camera view. This feature is rather unfriendly now that we have viewport render, as it takes several clicks to define a renderborder the same size as the camera.
It was decided to be removed a while ago, but seems to have been forgotten.
Old behavior: Selecting a renderborder enclosing the entire camera disabled render border.
New behavior: Selecting a renderborder enclosing the entire camera does not disable renderborder, it instead sets the renderborder to the camera. Selecting a renderborder completely outside the camera area (not intersecting the camera area at all), will disable render border. Renderborders the same size as the camera will allow full sample.