test(opennebula): remove test_get_field_nonecontext

Context values come exclusively from parse_shell_config which returns
Dict[str, str]. Shell variables can only be absent or hold string values,
so a None context value is impossible in production. The equivalent
realistic scenario is already covered by test_get_field_emptycontext.

Refs GH-6810

Author: mcanevet

tests/unittests/sources/test_opennebula.py

@@ -572,17 +572,6 @@ def test_get_field_emptycontext(self):
         val = net.get_field("eth9", "dummy")
         assert None is val
 
-    def test_get_field_nonecontext(self):
-        """
-        Verify get_field('device', 'name') returns None if context value is
-        None.
-        """
-        # Deliberately passing None value to test defensive handling in get_field
-        context = {"ETH9_DUMMY": None}
-        net = ds.OpenNebulaNetwork(context, mock.Mock())  # type: ignore[arg-type]
-        val = net.get_field("eth9", "dummy")
-        assert None is val
-
     @mock.patch(DS_PATH + ".get_physical_nics_by_mac")
     def test_gen_conf_gateway(self, m_get_phys_by_mac):
         """Test rendering with/without IPv4 gateway"""