Organize repo, remove obsolete code and data

[xee5ch]

User Story

As a developer of OSCAL based tooling, I want a reorganize the repo to remove extraneous and obsolete code from the current stable version of OSCAL and older versions that are likely unused.

Goals

• Simplify development of OSCAL models
• Make it faster and easier to access code in the repository

Dependencies

No response

Acceptance Criteria

• All OSCAL website and readme documentation affected by the changes in this issue have been updated. Changes to the OSCAL website can be made in the docs/content directory of your branch.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

(For reviewers: The wiki has guidance on code review and overall issue review for completeness.)

Revisions

No response