Remove clang pin for non-osx builds

[apmorton]

Checklist

• [x] Used a personal fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [x] Reset the build number to 0 (if the version changed)
• [ ] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

I believe the motivation for this pin is: https://bugreports.qt.io/browse/PYSIDE-2288 - which has been marked resolved since 6.5.1 See: https://github.com/conda-forge/qt-main-feedstock/pull/234

[apmorton]

@conda-forge-admin, please rerender

[conda-forge-webservices[bot]]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[apmorton]

Dup of #215