qom/cpu: Simplify how CPUClass::dump_statistics() prints

CPUClass method dump_statistics() takes an fprintf()-like callback and
a FILE * to pass to it.

Its only caller hmp_info_cpustats() (via cpu_dump_statistics()) passes
monitor_fprintf() and the current monitor cast to FILE *.
monitor_fprintf() casts it right back, and is otherwise identical to
monitor_printf().  The type-punning is ugly.

Drop the callback, and call qemu_printf() instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190417191805.28198-13-armbru@redhat.com>