Also remove unneeded default dtors.

Those are automatically generated.

This is automatic replacement with
ag '(?<!std::)size_t(?!\w)' --ignore-dir=ThirdParty -l | xargs perl -pi.bak -e  's/(?<!std::)size_t(?!\w)/std::size_t/g'

move findUnusedMeshNodes in MeshValidation to NodeSearch, replace removeUnusedMeshNodes() with removeNodes()

Since MinimalBoundingSphere uses MathLib::Point instead of GeoLib::Point.