[ARCH] Remove empty /guests from all DTS files

Currently, guest instance are created at boot-time using boot command
or using managment terminal commands. All guest instance have their
device tree under /guests node hence all DTS files had an empty /guests
node to make sure /guests node is always there.

Recently, we had a patch to ensure that /guests and /templates nodes
are present at boot-time before creating guest instances hence having
empty /guests node in DTS file is now redundant. This patch removes
empty /guests node from all DTS files.

Signed-off-by: Anup Patel <anup@brainfault.org>