Even though we can enable and disable xmon at runtime now, there are a
few places in the merge tree that call xmon and xmon_printf directly.

In the case below we call die() which will call xmon if it is enabled.

Also remove an unnecessary include of xmon.h in smp.c.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>