ENH: remove specialisations for scalar symmetry/transform patch fields

- previously used template specialisations, but now simply check
  pTrait<Type>::rank == 0. This aids for future extension to support
  other scalar-like fields.

src/finiteArea/fields/faPatchFields/basic/transform/transformFaPatchField.C

@@ -86,6 +86,12 @@ Foam::transformFaPatchField<Type>::valueInternalCoeffs
     const tmp<scalarField>&
 ) const
 {
+    if (pTraits<Type>::rank == 0)
+    {
+        // Transform-invariant types
+        return tmp<Field<Type>>::New(this->size(), pTraits<Type>::one);
+    }
+
     return pTraits<Type>::one - snGradTransformDiag();
 }
 
@@ -111,6 +117,12 @@ template<class Type>
 Foam::tmp<Foam::Field<Type>>
 Foam::transformFaPatchField<Type>::gradientInternalCoeffs() const
 {
+    if (pTraits<Type>::rank == 0)
+    {
+        // Transform-invariant types
+        return tmp<Field<Type>>::New(this->size(), Zero);
+    }
+
     return -this->patch().deltaCoeffs()*snGradTransformDiag();
 }