[MatL] Solids; Move up createMatStateVars().

The default implementation is sufficient for classes,
which don't do anything special with
the MaterialStateVariables.

MaterialLib/SolidModels/LinearElasticIsotropic.h

@@ -64,15 +64,6 @@ public:
     {
     };
 
-    std::unique_ptr<
-        typename MechanicsBase<DisplacementDim>::MaterialStateVariables>
-    createMaterialStateVariables() const override
-    {
-        return std::unique_ptr<
-            typename MechanicsBase<DisplacementDim>::MaterialStateVariables>{
-            new MaterialStateVariables};
-    }
-
 public:
     static int const KelvinVectorSize =
         MathLib::KelvinVector::KelvinVectorDimensions<DisplacementDim>::value;

MaterialLib/SolidModels/LinearElasticOrthotropic.h

@@ -128,15 +128,6 @@ public:
     {
     };
 
-    std::unique_ptr<
-        typename MechanicsBase<DisplacementDim>::MaterialStateVariables>
-    createMaterialStateVariables() const override
-    {
-        return std::unique_ptr<
-            typename MechanicsBase<DisplacementDim>::MaterialStateVariables>{
-            new MaterialStateVariables};
-    }
-
 public:
     static int const KelvinVectorSize =
         MathLib::KelvinVector::KelvinVectorDimensions<DisplacementDim>::value;

MaterialLib/SolidModels/MechanicsBase.h

@@ -63,7 +63,10 @@ struct MechanicsBase
     /// Polymorphic creator for MaterialStateVariables objects specific for a
     /// material model.
     virtual std::unique_ptr<MaterialStateVariables>
-    createMaterialStateVariables() const = 0;
+    createMaterialStateVariables() const
+    {
+        return std::make_unique<MaterialStateVariables>();
+    }
 
     using KelvinVector =
         MathLib::KelvinVector::KelvinVectorType<DisplacementDim>;