Make `warn` deprecation note a comment instead

What does this MR do?

We realized that issuing deprecation notices via Kernel.warn is quite noisy, as they also surface in tests, and since furthermore we already have a dedicated issue to migrate these functions over in #207989 (closed), it is probably safe to just make this a comment again, as it had been initially.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content