chore(schemas): drop orphaned mass-VM schemas left by the vm_ids route removal

[pparage]

#113 removed the six /v0/admin/proxmox/vms/vm_ids/* mass-operation routes and deleted the whole app/schemas/bundles package alongside them, but the mass-VM schemas in app/schemas/vms.py were left behind with no remaining caller:

• MassDeleteRequest, MassDeleteReply, MassDeleteVmItem
• MassActionRequest, MassActionReply
• aliases Request_ProxmoxVmsVmIds_* / Reply_ProxmoxVmsVmIds_*

$ grep -rn "MassDeleteRequest\|MassActionRequest\|Request_ProxmoxVmsVmIds" app/ --include=*.py | grep -v app/schemas/vms.py
(no output)

Only tests/test_schemas.py still references them (3 tests), so those go too. Inconsistent with how the bundle schemas were handled in the same PR.

app/schemas/vms.py:664 also has a stray module-level binding vm = MassDeleteVmItem that looks like a leftover and should go regardless.

Purely additive-risk-free cleanup; no API surface change (the routes are already gone).

[pparage]

Closed by #135.