Removed is_autocommi() from client_service interface as it is not

quite useful as there might not be enough information for it
after the statement has been processed. Better to handle retrying
on DBMS side. Also removed after_statement_result enumeration and
return plain int from after_statement().

dbsim/db_client_service.hpp

@@ -20,11 +20,6 @@ namespace db
             , client_state_(client_state)
         { }
 
-        bool is_autocommit() const override
-        {
-            return client_state_.is_autocommit();
-        }
-
         bool do_2pc() const override
         {
             return client_state_.do_2pc();