change rviz to no longer use opencv

[wjwwood]

This would avoid issues with linking against OpenCV on Jessie which uses Qt4. It looks like the process may have already been done, but the dependencies were never removed?:

From https://github.com/ros-visualization/rviz/blob/kinetic-devel/src/rviz/default_plugin/depth_cloud_mld.cpp#L137-L139:

// The following computation of center_x,y and fx,fy duplicates
// code in the image_geometry package, but this avoids dependency
// on OpenCV, which simplifies releasing rviz.

[wjwwood]

@tfoote @vrabaud this resolves the Qt5/Qt4 issues with rviz on Jessie in my local VM. Turns out rviz doesn't use image_geometry any more and was unnecessarily linking against it...

See ros/rosdistro#11488 (comment)

[tfoote]

that's convenient!