docs: inner hits is no longer experimental

docs/reference/search/request/inner-hits.asciidoc

@@ -1,8 +1,6 @@
 [[search-request-inner-hits]]
 === Inner hits
 
-experimental[]
-
 The <<mapping-parent-field, parent/child>> and <<nested, nested>> features allow the return of documents that
 have matches in a different scope. In the parent/child case, parent document are returned based on matches in child
 documents or child document are returned based on matches in parent documents. In the nested case, documents are returned