qmp: Eliminate silly QERR_COMMAND_NOT_FOUND macro

The QERR_ macros are leftovers from the days of "rich" error objects.
They're used with error_set() and qerror_report(), and expand into the
first *two* arguments.  This trickiness has become pointless.  Clean
this one up.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/monitor.c b/monitor.c
index 2ac40c9..2e2b0e5 100644
--- a/monitor.c
+++ b/monitor.c
@@ -5081,7 +5081,8 @@
     trace_handle_qmp_command(mon, cmd_name);
     cmd = qmp_find_cmd(cmd_name);
     if (!cmd || invalid_qmp_mode(mon, cmd)) {
-        qerror_report(QERR_COMMAND_NOT_FOUND, cmd_name);
+        qerror_report(ERROR_CLASS_COMMAND_NOT_FOUND,
+                      "The command %s has not been found", cmd_name);
         goto err_out;
     }