monitor: drop unused monitor debug code

monitor: drop unused monitor debug code

In the old QMP days, this code was used to find out QMP commands that
might be calling monitor_printf() down its call chain.

This is almost impossible to happen today, because the qapi converted
commands don't even have a monitor object. Besides, it's been more than
a year since I used this last time.

Let's just drop it.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>