ENH: Migrate TextureFeatures content to ITK main; archive this repo

[hjmjohnson]

The TextureFeatures module has been ingested into ITK main via InsightSoftwareConsortium/ITK#6238 (merge commit b6eb189e64). This PR removes the now-duplicated content from this upstream repo and promotes the migration notice to the README so the GitHub landing page reflects the archived status.

Recommendation for the repo owner: after merging this PR, mark this repository Archived under repo Settings -> Danger Zone. The pre-ingest git history remains intact for blame/archaeology.

What this PR does

Per the ITK ingestion strategy, the upstream repo's tree tip should stop carrying a second copy of the same files (ODR).

Removed: include/, test/, wrapping/, CMakeLists.txt, itk-module.cmake, CTestConfig.cmake

README handling: the migration notice is now README.md at the repo root (so the GitHub landing page renders it). Any prior README.rst is preserved as info.rst.

Preserved: full pre-ingest git history.

Archive checklist for the maintainer

1. Review and merge this PR.
2. Settings -> General -> Danger Zone -> Archive this repository.
3. (Optional) Pin a link to the ITK in-tree location in the repo description.