Remove the GLUED, STRETCHABLE mentions in the NAD code

[So-Fras]

Describe the current behavior

Some parts of the NAD code were introduced to deal with node moving (#457) but the feature does not use the introduced code in the end.

Describe the expected behavior

We could lighten the code by removing (for example) the GLUED_CLASS, the STRETCHABLE_CLASS and the GLUED_CENTER_CLASS.
Everything that was introduced in the #457 PR and that is not used should be removed.

Describe the steps

No response

Environment

powsybl-diagram 4.7.0

Relevant Log Output

No response

Extra Information

Some attention should be paid on whether the introduced code is not used in the powsybl-network-viewer repository anyway.