Update vortex dipole case to use new format and diagnostics

src/cases/dipole/spins.conf

+## Vortex dipole configuration file
+
+# Spatial Parameters
+Lx = 2.0
+Ly = 1.0
+Lz = 2.0
+Nx = 256
+Ny = 1
+Nz = 256
+min_x = -1
+min_y = 0
+min_z = 0
+
+# Expansion types
+type_x = NO_SLIP
+type_y = FREE_SLIP
+type_z = NO_SLIP
+
+# Physical Parameters
+rho_0 = 1000.0
+visco = 8e-4
+
+# Problem Parameters
+U0 = 299.5284
+X1 = -0.1
+Z1 = 1.0
+X2 = 0.1
+Z2 = 1.0
+r0 = 0.1
+
+# Temporal Parameters
+final_time = 1.5
+plot_interval = 0.05
+#dt_max = 0.0
+
+# Restart Options
+restart = false
+restart_time = 0.0
+restart_sequence = 0
+restart_from_dump = false
+compute_time = -1
+
+# Perturbation Parameter
+perturb = 0e-3
+
+# Filter Parameters
+f_cutoff = 0.6
+f_order = 2.0
+f_strength = 20.0
+
+# secondary diagnostics
+#compute_enstrophy = true
+#compute_dissipation = true
+#compute_BPE = true
+#compute_internal_to_BPE = true
+compute_stresses_top = true
+compute_stresses_bottom = true

src/cases/kh_billow/kh_billow.cpp

@@ -80,7 +80,6 @@ double N2_max;
 class userControl : public BaseCase {
     public:
         // Grid and topography arrays
-        DTArray *zgrid;                 // Full grid fields
         Array<double,1> xx, yy, zz;     // 1D grid vectors
         DTArray *Hprime;                // derivative of topography vector