py/emitglue: Host definition of mp_verbose_flag.

This may not seem like the ideal place, but is actually the only place
in py/ where it gets referenced, so is just right.

lib/utils/printf.c

@@ -48,8 +48,6 @@ int vprintf(const char *fmt, va_list ap) {
 }
 
 #if MICROPY_DEBUG_PRINTERS
-mp_uint_t mp_verbose_flag = 1;
-
 int DEBUG_printf(const char *fmt, ...) {
     va_list ap;
     va_start(ap, fmt);