Remove a duplicate mapping

(cherry picked from commit c3c31a6)

Author: michaelklishin

deps/rabbit/priv/schema/rabbit.schema

@@ -712,10 +712,6 @@ end}.
     {datatype, {list, atom}}
 ]}.
 
-{mapping, "default_users.$name.password", "rabbit.default_users", [
-    {datatype, string}
-]}.
-
 {translation, "rabbit.default_users", fun(Conf) ->
     case rabbit_cuttlefish:aggregate_props(Conf, ["default_users"]) of
         [] -> cuttlefish:unset();