Bug#45989 memory leak after explain encounters an error in the query

the fix is reverted from 5.1, mysql-pe as 
unnecessary(no valgrind warnings there).

sql/sql_select.cc

@@ -2248,7 +2248,7 @@ JOIN::destroy()
 	tab->cleanup();
     }
     tmp_join->tmp_join= 0;
-    tmp_table_param.cleanup();
+    tmp_table_param.copy_field= 0;
     DBUG_RETURN(tmp_join->destroy());
   }
   cond_equal= 0;