ZTS: Get rid of old Ubuntu runners

[tonyhutter]

Motivation and Context

Remove unneeded github runners.

Description

Remove the old Ubuntu 'sanity' and part1-4 tests. These are no longer needed since we now test Ubuntu under the QEMU runners. This should free up some runners.

How Has This Been Tested?

github runners willt est

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[tonyhutter]

Closing in favor of: #16549