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_netgear/netgear_plus.py

@@ -786,14 +786,6 @@ class NetgearPlusDriver(SwitchDriver):
                 warnings.append(
                     {
                         "code": "firmware_update_available",
-                        "severity": "warning",
-                        "title": "Firmware update available",
-                        "message": (
-                            f"Version {latest_fw} is available for {model_name} "
-                            f"(installed: {current_fw})."
-                        ),
-                        "action": None,
-                        "action_label": None,
                         "meta": {
                             "download_url": (
                                 f"{_FW_CDN_BASE}/{model_name}"