v3.0: remove the deprecated code #57

Remove the code deprecated in the 2.x minor versions, as cleverage/process-bundle#292 does for process-bundle v6.0.

Common to the bridges:

• Remove the deprecated aliases of the service ids (cleverage_archive_process.*); the tasks become private services (remove public: true and the container.private tag).
• Reject any key under cleverage_archive_process (remove the trigger_deprecation() of the extension, CleverAgeArchiveProcessExtension l.36).
• @final since → final.
• Remove the paragraph about the deprecations from docs/index.md.
• Write UPGRADE-3.0.md.

Specific to this bundle:

• Aliases cleverage_archive_process.task.zip / .unzip (config/services/task.yaml).
• final: ZipTask, UnzipTask, CleverAgeArchiveProcessBundle.
• Attach PR cleverage/process-bundle#143 - ZipTask and UnzipTask: compatibility with process-bundle v6.0 #24 (process-bundle v6.0) to this major version.

Found during the global audit after the releases (bridges-audit.md #140).