[CMake] Remove Qt from all configurations

[bakpaul]

• Remove its presence from postinstall scripts
• Remove it from pixi
• Remove it from nix

Unrelated to this PR, but Clang compilation is broken because of binding compilaiton failing. This is to test the PR
[ci-depends-on https://github.com/sofa-framework/SofaPython3/pull/608]

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By submitting this pull request, I acknowledge that
I have read, understand, and agree SOFA Developer Certificate of Origin (DCO).

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[hugtalbot]

In CI I trust 👍

[sofabot]

[ci-depends-on] detected during build #4.

To unlock the merge button, you must

• Merge or close Fix Clang compilation SofaPython3#608
  For this build, the following CMake flags will be set
  -DSOFAPYTHON3_GIT_REPOSITORY='https://github.com/sofa-framework/SofaPython3'
  -DSOFAPYTHON3_GIT_TAG='fb0e02f9aea12af25936150c398f1004ad4b3165'