ENH: use unique_ptr for resource handling in dynamicMesh

ENH: defaulting for destructors where possible

STYLE: clear() instead of setSize(0) for plain Lists

STYLE: use bool operator instead of valid()/empty() for autoPtr tests

src/dynamicMesh/motionSmoother/polyMeshGeometry/polyMeshGeometry.C

@@ -324,7 +324,6 @@ bool Foam::polyMeshGeometry::checkFaceTet
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
-// Construct from components
 Foam::polyMeshGeometry::polyMeshGeometry(const polyMesh& mesh)
 :
     mesh_(mesh)