Small cleanup of derived tables handling.

We should not call free_tmp_table() for derived table in 
mysql_derived_filling(), since by this moment this table is already
registered in THD::derived_tables list and thus free_tmp_table() will
be called for it automatically in close_thread_tables().


sql/sql_derived.cc:
  We should not call free_tmp_table() for derived table in 
  mysql_derived_filling(), since by this moment this table is already
  registered in THD::derived_tables list and thus free_tmp_table() will
  be called for it automatically in close_thread_tables().

sql/sql_derived.cc

@@ -268,13 +268,8 @@ int mysql_derived_filling(THD *thd, LEX *lex, TABLE_LIST *orig_table_list)
         unit->cleanup();
     }
     else
-    {
-      free_tmp_table(thd, table);
       unit->cleanup();
-    }
     lex->current_select= save_current_select;
-    if (res)
-      free_tmp_table(thd, table);
   }
   return res;
 }