refactor(warnings): report raw signal only, no severity/presentation

get_device_warnings() now returns only {code, meta} — severity, title,
message, and action are resolved centrally by netork's
WARNING_CATALOG (netork/core/device_warnings.py), not by the driver.
Keeps this driver independent of netork and avoids per-vendor drift in
how the same warning code is presented.

napalm_openmediavault/openmediavault.py

@@ -104,8 +104,6 @@ class OpenMediaVaultDriver(LinuxDriver):
         if updates:
             warnings.append({
                 "code": "updates_available",
-                "severity": "warning",
-                "action": None,
                 "meta": {
                     "count": upgradable_count,
                     "packages": [u.get("name", "") for u in updates[:10]],