Fix vtkThinPlateSplineTransform for coplanar point configurations

vtkThinPlateSplineTransform provided incorrect output when all the source points were coplanar and/or target points were coplanar and one of the planes were exactly at aligned with coordinate system axes. Root cause was that in this case the A linear transformation matrix in vtkThinPlateSplineTransform::InternalUpdate was singular and it was "regularized" by setting it to identity.

Based on reviewing the code and results of the added "TestThinPlateSplineTransform" test, this regularization does not seem necessary. It breaks computation of forward transform and it does not improve chances that the inverse transform can be computed successfully.