Remove old cilantro/ui/concept/workspace file

This file was ported to JavaScript a while ago and is no longer necessary. The JS file is [here](https://github.com/cbmi/cilantro/blob/2f7dd45afc725f1f4df003228197ebaf80df38e6/src/js/cilantro/ui/concept/workspace.js).

Signed-off-by: Don Naegely <naegelyd@gmail.com>