Remove ColumnDescriptor structure and usage

The ColumnDescriptor data structure (column_descriptor.py) was introduced to support the server-side equivalent data structure which has been serialized in the tree structure by the Trace Compass trace server. However, this was an undocumented and Trace Compass internal data structure. The serialization was removed to align with the TSP specification. After that it's no longer available on the client and cannot be acted on.

In implementation of option --get-tree, the column descriptor is used to print the header information of each column. Since it's not available anymore the header is not printed anymore.

When removing this data structure in the client, the print-out (TreeModel.print()) needs to be fixed as well to print the header information which is provided differently now.

Commencez par column_descriptor.py et l’implémentation de --get-tree, puis examinez TreeModel.print() pour retracer la manière dont les en-têtes de colonnes sont actuellement générés. Supprimez la structure obsolète et ses utilisations, puis vérifiez que --get-tree et TreeModel.print() produisent toujours l’en-tête de chaque colonne à l’aide des informations désormais fournies par la spécification TSP.

Rédigé par le modèle d'indexation à partir du texte de l'issue.