trace: Simplify how st_print_trace_file_status() prints

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

Its only caller hmp_trace_file() 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: <20190417191805.28198-3-armbru@redhat.com>