Removing references to incompressible_solid in sofc.cti

Removes references to incompressible_solid phase in the codebase.
This phase type references ConstDensityThermo phase, which is a
non-physical model and is to be deprecated, with Cantera 2.5. In
order to enable deprecation, the following changes are hereby made:

- Changes oxide_bulk phase type from incompressible_solid to lattice in sofc.cti
- Changes test_convert.py so that it interrogates the density_mole of the bulk_oxide, rather than density_mass

data/inputs/sofc.cti

@@ -108,10 +108,10 @@ species( name = "electron",   atoms = "E:1",
 # consider the oxygen sublattice. The only species we define are a
 # lattice oxygen, and an oxygen vacancy. Again, the density is a
 # required input, but is not used here, so may be set arbitrarily.
-incompressible_solid(name = "oxide_bulk",
+lattice(name = "oxide_bulk",
       elements = "O E",
       species = "Ox VO**",
-      density = (0.7, 'g/cm3'),
+      site_density = (0.0176, 'g/cm3'),
       initial_state = state( temperature = tt,
                              pressure = OneAtm,
                              mole_fractions = "Ox:0.95 VO**:0.05")

interfaces/cython/cantera/test/test_convert.py

@@ -496,7 +496,7 @@ class CtmlConverterTest(utilities.CanteraTest):
 
         self.assertNear(gas_a.P, ct.one_atm)
         self.assertNear(anode_bulk['electron'].X, 1.0)
-        self.assertNear(oxide_a.density, 700)
+        self.assertNear(oxide_a.density_mole, 17.6)
 
     def test_diamond(self):
         gas, solid = ct.import_phases('diamond.cti', ['gas','diamond'])