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_opnsense/opnsense.py

@@ -1729,8 +1729,6 @@ class OPNsenseDriver(FirewallDriver):
                 if upgrades:
                     warnings.append({
                         "code": "updates_available",
-                        "severity": "info",
-                        "action": None,
                         "meta": {
                             "count": len(upgrades),
                             "packages": [u.get("name", "") for u in upgrades[:10]],