chore: expose advanced_search flag in super_admin UI for self-hosted (#14750)

## Description

Removes `chatwoot_internal: true` from the `advanced_search` feature
flag so self-hosted enterprise userss can toggle it from the super_admin
UI instead of going through a rails console.

config/features.yml

@@ -200,7 +200,6 @@
   display_name: Advanced Search
   enabled: false
   premium: true
-  chatwoot_internal: true
 - name: saml
   display_name: SAML
   enabled: false