migration: move migration_global_dump() to migration-hmp-cmds.c

It is only used there, so we can make it static.
Once there, remove spice.h that it is not used.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

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fix David Edmonson ui/qemu-spice.h unintended removal