Remove the unused UserFlags type

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/sharp-meals-fetch.md

@@ -0,0 +1,5 @@
+---
+'@backstage/core-plugin-api': minor
+---
+
+Removed the unused `UserFlags` type.

packages/core-plugin-api/api-report.md

@@ -799,9 +799,6 @@ export function useElementFilter<T>(
   dependencies?: any[],
 ): T;
 
-// @public
-export type UserFlags = {};
-
 // @public
 export function useRouteRef<Optional extends boolean, Params extends AnyParams>(
   routeRef: ExternalRouteRef<Params, Optional>,

packages/core-plugin-api/src/apis/definitions/FeatureFlagsApi.ts

@@ -61,13 +61,6 @@ export type FeatureFlagsSaveOptions = {
   merge?: boolean;
 };
 
-/**
- * User flags alias.
- *
- * @public
- */
-export type UserFlags = {};
-
 /**
  * The feature flags API is used to toggle functionality to users across plugins and Backstage.
  *