Remove leftover feature flag (#81699)

rest-api-spec/src/main/resources/rest-api-spec/api/eql.search.json

@@ -5,8 +5,7 @@
       "description": "Returns results matching a query expressed in Event Query Language (EQL)"
     },
     "stability": "stable",
-    "visibility":"feature_flag",
-    "feature_flag":"es.eql_feature_flag_registered",
+    "visibility":"public",
     "headers":{
       "accept": [ "application/json"],
       "content_type": ["application/json"]