Remove python2 support from Mariner

[oliviacrain]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/tools/cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./SPECS/LICENSES-AND-NOTICES/data/licenses.json, ./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

Python 2 end-of-life was January 1, 2020. Python 2 no longer receives security updates from upstream, which hurts our security posture. Additionally, many packages are dropping support for Python 2, which makes maintaining Python 2 support a burden on our package upgrade efforts.

So, in light of that, let's remove our python2 package!

Thanks to a lot of incremental python2 removal work across the past few months, we are finally in a position where removal is possible. This PR removes the python2 package, alongside python2 subpackages and macros.

Change Log

• Remove python2
• Remove the python2-only packages python-setuptools and python-pip
• Remove python2-related RPM/SRPM macros from mariner-rpm-macros
• Remove python2 subpackages from python-six, python-setuptools_scm
• Remove faulty python2-setuptools requirement in mercurial

Does this affect the toolchain?

YES

Test Methodology

• Pipeline build ongoing