feat: drop the get_device_warnings override; the pending updates are the fact (0.2.0)

The override counted "N upgraded" in an apt simulation run without a
fixed locale -- nothing matched on a German host -- and hid held-back
packages, which FULL_UPGRADE installs. netOrk names updates_available
from get_available_updates (netOrk #1111).

tests/test_no_warnings.py

@@ -0,0 +1,12 @@
+"""The pending updates are a fact, not a warning of the driver's (netOrk #1111).
+
+The override counted "N upgraded" in apt's simulation -- nothing on a German
+host -- and hid held-back packages, which FULL_UPGRADE installs. The caller
+names updates_available from get_available_updates.
+"""
+
+from napalm_openmediavault.openmediavault import OpenMediaVaultDriver
+
+
+def test_no_warnings_of_its_own():
+    assert "get_device_warnings" not in vars(OpenMediaVaultDriver)