[DOCS] Lookup runtime fields are now GA (#114221) (#114229)

(cherry picked from commit 1292580c0333a4f7402cb0d133f2a991a5302d1b)

docs/reference/mapping/runtime.asciidoc

@@ -821,8 +821,6 @@ address.
 [[lookup-runtime-fields]]
 ==== Retrieve fields from related indices
 
-experimental[]
-
 The <<search-fields,`fields`>> parameter on the `_search` API can also be used to retrieve fields from
 the related indices via runtime fields with a type of `lookup`.