build: removing reredirect sphinx extension

[germa89]

Description

This is extension is no longer used (or at least I couldn't make it work properly ... almost ever).

Furthermore, with the change in the domain at the higher level, I dont think this extension is explicable for the current cases.

Issue linked

Close #3216

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.62%. Comparing base (587a0cb) to head (ed27293).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3224      +/-   ##
==========================================
- Coverage   82.67%   82.62%   -0.05%     
==========================================
  Files          53       53              
  Lines        9625     9625              
==========================================
- Hits         7957     7953       -4     
- Misses       1668     1672       +4     

[germa89]

I just realised that this documentation was wrongly set. It was redirecting the krylov user guide to a broken link.

So the extension works, but now it is not needed.

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬

[germa89]

The branch check will never pass until a new branch and PR is set. Sooo... I'm merging anyway.