Blender Git Loki

Subsurf: Remove OpenSubdiv options from modifier

There are following reasons to do so:

- The plan is to replace it with some sort of object or viewport option,
so we can apply OpenSubdiv subdivisions on top of modifier stack and
keep modifier stack purely CPU side.

This will solve issues when adding some relation in scene will force
modifier to be evaluated on CPU.

- With new upcoming OpenSubdiv based CPU modifier implementation we can
cache topology similar to what GPU side was doing, which will already
be reasonably faster.

- OpenSubdiv GPU does not work since the OpenGL version bump, and is
to be rewritten with all the adaptive refine options kept in mind.

Since OpenSubdiv GPU was already broken and was only causing object
to become invisible, there is no reason to keep having that option in
the modifier.

Reviewers: brecht

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D3598