[Docs] Remove obsolete Memory configuration guidance

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Telegram.

What changed

• remove the obsolete claim that Settings > Memory ends with a model Configuration card
• keep the adjacent operator guidance for the sections that the current page actually renders

Why this change was made

The Memory settings UI and its focused render test explicitly removed the model Configuration section, but the public Memory guide still told administrators to look for it.

Impact

Administrators now see public guidance that matches the shipped Memory settings page. This is a documentation-only correction; model configuration remains documented through the applicable environment variables.

Screenshots

[roomote-community]

No code issues found. See task

_{Reviewed 262b95b}