Document deprecated or non-working function arguments

https://github.com/zarr-developers/zarr-python/pull/2596#discussion_r1900925415 has a list of function arguments that still exist, but no longer do anything (or raise errors) in v3. The API docs don't say anything about them not working though (e.g., see `zarr.synchronous.create`), giving the misleading impression they do work.

We should update the docs to mark these as non-functional.