pvecm: remove mtunnel

pvecm: remove mtunnel

it was a mistake to move it here in the first place, and now we can
finally drop it again, as no PVE version can exist in 6.0, or latest
5.4 which still tries to use this one.
The one we will keep using is the one in qm from qemu-server, as
there we have full access to all it's perl modules without adding
cyclic dependencies.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>