[docs] Remove deprecated ui:rootFieldId option

Author: x0k

apps/docs/src/content/docs/api-reference/ui-schema.mdx

@@ -28,7 +28,6 @@ Each UI schema node may contain the following fields:
 
 Root node of UI schema can have an additional fields:
 
-- `ui:rootFieldId` - prefix of generated field ids
 - `ui:globalOptions` - global ui options that are applied to all fields, are overwritten by `ui:options`.
 - `ui:submitButton` - submit button UI schema
 - `ui:formElement` - form element UI schema