md-cluster/raid10: don't call remove_and_add_spares during reshaping stage

remove_and_add_spares is not needed if reshape is
happening in another node, because raid10_add_disk
called inside raid10_start_reshape would handle the
role changes of disk. Plus, remove_and_add_spares
can't deal with the role change due to reshape.

Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>