docs: State that the legacy streaming API is removed in 4.0

[marcelomendoncasoares]

serverpod/serverpod#5544 removed the legacy streaming session and the deprecated streaming APIs. The streaming page still called them deprecated, and the session type table still listed StreamingSession, which no longer exists.

Rewords the section on the streaming page and drops the row from the session type table. The archive page keeps documenting the old API for readers on 3.x.

[developerjamiu]

Suggestion: 02-logging.md:41-50 documents a log table that serverpod/serverpod#5544 stopped filling. logMessage() had a single caller, in endpoint_websocket_request_handler.dart right after handleStreamMessage, and that file is gone.

The count and the cascade sentence go with the row:

In the database they land in three tables:

| Table | Holds |
| --- | --- |
| `serverpod_session_log` | One row per completed session. |
| `serverpod_log` | Your `session.log` messages. |
| `serverpod_query_log` | Database queries. |

The last two reference the session row, so deleting a session row removes its queries with it.

The model and the Insights read stay, so old rows are still queryable. Nothing on 4.0 writes new ones.