[19.0] Create branch to accept PR: remove obsolete 'documentation' user menu entry in disable_odoo_online

[heyagent]

• Impacted versions: 19.0
• Problem: In Odoo 19, the user menu no longer registers a 'documentation' item. The disable_odoo_online addon still removes it alongside 'support' and 'odoo_account'. The 'documentation' removal is now obsolete.
• Proposed change: Drop the removal of 'documentation' from static/src/js/user_menu_items.esm.js, and update the README to reflect that only 'support' and 'odoo_account' are removed.
• Notes: This is a small cleanup with no functional impact in 19.0 beyond avoiding a non-existent registry key.
• Request: Please create a 19.0 branch so I can submit the PR. I have the patch ready.