core-plugin-api: Deprecate unused types

Signed-off-by: Johan Haals <johan.haals@gmail.com>

.changeset/young-steaks-punch.md

@@ -0,0 +1,5 @@
+---
+'@backstage/core-plugin-api': patch
+---
+
+Deprecate unused ApiRef types

packages/core-plugin-api/src/apis/system/types.ts

@@ -35,6 +35,7 @@ export type AnyApiRef = ApiRef<unknown>;
  * Transforms ApiRef type into its inner API type.
  *
  * @public
+ * @deprecated unused type.
  */
 export type ApiRefType<T> = T extends ApiRef<infer U> ? U : never;
 
@@ -51,6 +52,7 @@ export type TypesToApiRefs<T> = { [key in keyof T]: ApiRef<T[key]> };
  * Reverse type transform of {@link TypesToApiRefs}.
  *
  * @public
+ * @deprecated unused type.
  */
 export type ApiRefsToTypes<T extends { [key in string]: ApiRef<unknown> }> = {
   [key in keyof T]: ApiRefType<T[key]>;