[PlanarLayout] fix persistence array

[MatPont]

This PR fixes #966 by fixing the code introduced in #944.

• Problem: The PR [MT-PGA] refactor and convert to diagram feature #944 added arrays encoding persistence for nodes and arcs in the vtk output (it was related to the feature to manage persistence diagrams).
  However, persistence arrays already existed in the code, resulting in an overwrite (only one vtk array with the same name can exists).
  The persistence arrays that remained at the end of the algorithm worked only for persistence diagrams and not for merge trees.
• Solution: the duplicated arrays encoding persistence are removed, and the already existing arrays are generalized to take into account the fact that persistence diagrams can be used.

[julien-tierny]

wonderful, thanks!