Clipper was essentially a static class used from an object.
Changed it to actually being fully static and removed the
Clipper member from the Renderer class.

Change-Id: I146a9966317cfa9f73e679c7b471873cdd030122
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/30951Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>