Moving the lid-driven cavity test from the combined module to Navier-Stokes.

Closes #3036.
Removing dummy 'simple diffusion' test from Navier-Stokes module.

Refs #3036.
Merge pull request #3097 from jwpeterson/move_ins

Move the Navier-Stokes test out of combined
Merge commit '1a728cb9c302638479c2489d832144ca6dff69fd'