New issue 1324: Shouldn't need to demote 2nd order tets in CartesianCoordinateHandler.pixelize https://bitbucket.org/yt_analysis/yt/issues/1324/shouldnt-need-to-demote-2nd...
Hypothetically, #2401 should make it so we don't have to demote second order tets when slicing through a 3D mesh, e.g. this check:
`elif field_data.shape == 10`
should be removable. I would like to test this first though.