add deprecation log (#12674)

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #12674
| License       | MIT
| Doc PR        | 

Hmm, then since this whole BC warning thing is meant to be helpful to *most* people, I agree and think we should revert this. For framework-users relying on the old API, there will be deprecation warnings triggered elsewhere.