I understand the use case on this. You want to reduce the total number of items displayed on the animation palette.

It appears to be an issue with how the animation palette works. The Left Foot entry will still display in the Hierarchy window as seen in the right side of the above image. It will also display in the Animation Palette windows.

Hiding a parameter will hide it from the animation palette. Hiding an actor will not hide it from the animation palette.

I hid all the parameters of Left Foot and then I hid Left Foot itself. The result I got is shown in the image above.