[FEM] Elmer: fix default for heat

- revert change from comm it commit 117d789e - "None" is the correct default. (I mixed this up with Navier-Stokes)

src/Mod/Fem/femsolver/elmer/equations/heat.py

@@ -72,7 +72,7 @@ class Proxy(nonlinear.Proxy, equationbase.HeatProxy):
         obj.Bubbles = True
         obj.Stabilize = False
         obj.Convection = CONVECTION_TYPE
-        obj.Convection = "Computed"
+        obj.Convection = "None"
         obj.PhaseChangeModel = PHASE_CHANGE_MODEL
         obj.PhaseChangeModel = "None"
         obj.Priority = 20

src/Mod/Fem/femsolver/elmer/writer.py

@@ -448,7 +448,7 @@ class Writer(object):
                 "Type of convection to be used"
             )
             equation.Convection = heat.CONVECTION_TYPE
-            equation.Convection = "Computed"
+            equation.Convection = "None"
         if not hasattr(equation, "PhaseChangeModel"):
             equation.addProperty(
                 "App::PropertyEnumeration",