Revert "Install OpenGL on TravisCI, for #229."
Revert "Install OpenGL on TravisCI, for #229."

This reverts commit fd0f536

donkirkby/live-py-plugin,brandm/live-py-plugin,donkirkby/live-py-plugin,brandm/live-py-plugin,donkirkby/live-py-plugin,brandm/live-py-plugin,brandm/live-py-plugin,brandm/live-py-plugin,donkirkby/live-py-plugin,donkirkby/live-py-plugin