removed code relative to cnecs in series with a pst

[phiedw]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem?

No

What kind of change does this PR introduce?

Removing a feature for which the specifications were misunderstood

What is the current behavior?

We do not include in the functional part of the objective function cnecs that are linked with a pst in the "do-not-optimize-cnec-secured-by-its-pst" parameter, when taps would be sufficient to solve constraints on that cnec. This isn't exactly what the TSOs wanted.

What is the new behavior (if this is a feature change)? The feature is removed.

Does this PR introduce a breaking change or deprecate an API?

• [x] Yes
• [ ] No

If yes, please check if the following requirements are fulfilled

• [x] The Breaking Change or Deprecated label has been added
• [x] The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

You should remove the parameter "do-not-optimize-cnec-secured-by-its-pst". If you were using that feature, please contact us so we can understand why you were using this feature, and what exactly the need for it is on your end, so we can try find a better solution for you.

Other information:

[phiedw]

I'm not sure what relevant test I could add.