Adjust the 3D tests

test/sumfact/stokes/stokes_3d_dg.mini

-__name = sumfact_stokes_3d_dg_{__exec_suffix}
-__exec_suffix = symdiff, numdiff | expand num
+__name = sumfact_stokes_3d_dg
 
 cells = 4 4 4
 extension = 1. 1. 1.
@@ -10,10 +9,5 @@ name = {__name}
 extension = vtu
 
 [formcompiler]
-numerical_jacobian = 0, 1 | expand num
-exact_solution_expression = g
-compare_l2errorsquared = 1e-9
+numerical_jacobian = 0
 sumfact = 1
-
-# Disable symdiff test for now
-{__exec_suffix} == symdiff | exclude

test/sumfact/stokes/stokes_3d_dg.ufl

 cell = hexahedron
 
 x = SpatialCoordinate(cell)
-g_v = as_vector((4*x[1]*(1.-x[1]), 0.0, 0.0))
-g_p = 8*(1.-x[0])
-g = (g_v, g_p)
+g_v = as_vector((16.*x[1]*(1.-x[1])*x[2]*(1.-x[2]), 0.0, 0.0))
 bctype = conditional(x[0] < 1. - 1e-8, 1, 0)
 
 P2 = VectorElement("DG", cell, 2)