Remove all references to old dm-verity boot tooling

[dmcilvaney]

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)
• [ ] Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• [ ] 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/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
• [ ] If you are adding/removing a .spec file that has multiple-versions supported, please add @microsoft/cbl-mariner-multi-package-reviewers team as reviewer (Eg. golang has 2 versions 1.18, 1.21+)
• [ ] Ready to merge

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Summary

Remove the now pointless parts of https://github.com/microsoft/azurelinux/pull/549 (since https://github.com/microsoft/azurelinux/pull/9537 removed dm-verity support from the imager tool).

Some parts of #549 were general refractors which are still needed, but everything related to building an image with dm-verity enabled has been removed.

See #9537 for details on migration paths using the imagecustomizer tool

Change Log

• Remove ReadOnlyVerityRoot config struct
• Remove verity-read-only-root package
• Remove logic around verity roots in the toolkit

Does this affect the toolchain?

NO

Associated issues

• https://microsoft.visualstudio.com/DefaultCollection/OS/_workitems/edit/51951945

Test Methodology

• tbd