PAAPI deprecation

[Net-burst]

Google has deprecated PAAPI. We should also remove it to not pollute our codebase.

https://privacysandbox.com/news/update-on-plans-for-privacy-sandbox-technologies/

[bsardo]

Discussed at the PMC. There are no concerns with breaking PBS core code. There are a handful of adapters that appear to have PAAPI-specific logic. We should create a PR for each adapter to remove the PAAPI-specific logic and notify the maintainers and give some grace period before removing the core logic.