Revert #421: underscore prefix docs

app/spicedb/concepts/schema/page.mdx

@@ -594,35 +594,6 @@ Examples:
   resource, thus changing it from a simple relation to a _computed_ set of subjects.
 </Callout>
 
-### Private/Internal Identifiers
-
-SpiceDB supports using an underscore (`_`) prefix for identifiers to establish a convention for marking definitions, relations, or permissions as "private" or "internal". This is a naming convention only—they are not treated any different at runtime, and they can still be used in relationships and permission checks like
-any other identifier.
-
-```zed
-definition document {
-    relation viewer: user
-    relation _internal_viewer: user  // private: internal use only
-
-    permission _can_view = viewer + _internal_viewer  // private: synthetic
-    permission view = _can_view  // public API
-}
-```
-
-This convention is useful for:
-
-- **Synthetic permissions**: Permissions that exist only to compose other permissions
-- **Internal relations**: Relations not meant to be directly referenced by application code
-- **Implementation details**: Parts of your schema that may change without affecting the public API
-
-#### Identifier Rules
-
-- Identifiers can begin with a lowercase letter (`a-z`) or underscore (`_`)
-- After the first character, identifiers can contain lowercase letters, numbers, and underscores
-- Identifiers must be 3-64 characters long and end with an alphanumeric character
-- Valid: `_ab`, `_private`, `_internal_relation`, `_helper123`
-- Invalid: `_` (too short), `_a` (too short), `_trailing_` (cannot end with underscore)
-
 ## Notes on syntax
 
 ### Arrows vs Subject Relations