Migrated to ITK main

As of 2026-05-05, the IOMeshSTL module has been ingested into the main ITK repository at Modules/IO/IOMeshSTL and the standalone remote module is no longer maintained here.

• In-tree home: https://github.com/InsightSoftwareConsortium/ITK/tree/main/Modules/IO/IOMeshSTL
• Ingest PR: InsightSoftwareConsortium/ITK#6206
• Historical reference: the original README.rst content is preserved as info.rst.

Please file new issues and pull requests against the in-tree module.