Removal of lang_string_set_to_xml (dead code) (#457)

Previously, the serialization of `adapter.xml` uses the general
`object_to_xml_element()` method. In it, there was branch to a call of
`lang_string_set_to_xml()` without setting the tag parameter, which
would have caused an exception, if the code was ever run.

We decided to remove the call of `lang_string_set_to_xml` completely as 
this specific case in `object_to_xml()` is considered dead code, as the
XML tag for a `LangStringSet` varies based on its context 
(the tag is determined by the *parent's* attribute), it must always be 
called explicitly with a tag parameter by the *parent's serialization 
logic*. Since there is no scenario where a `LangStringSet` is 
serialized in isolation (It **cannot** be a standalone xml object), 
this branch is unreachable and should be removed to maintain code 
cleanliness. 

Fixes #397

Author: ZANDx1

sdk/basyx/aas/adapter/xml/xml_serialization.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2025 the Eclipse BaSyx Authors
+# Copyright (c) 2026 the Eclipse BaSyx Authors
 #
 # This program and the accompanying materials are made available under the terms of the MIT License, available in
 # the LICENSE file of this project.
@@ -899,10 +899,6 @@ def object_to_xml_element(obj: object) -> etree._Element:
         return value_reference_pair_to_xml(obj)
     elif isinstance(obj, model.ConceptDescription):
         return concept_description_to_xml(obj)
-    elif isinstance(obj, model.LangStringSet):
-        # FIXME: `lang_string_set_to_xml` expects `tag` parameter, `tag` doesn't have default value
-        # Issue: https://github.com/eclipse-basyx/basyx-python-sdk/issues/397
-        return lang_string_set_to_xml(obj)  # type: ignore[call-arg]
     elif isinstance(obj, model.EmbeddedDataSpecification):
         return embedded_data_specification_to_xml(obj)
     elif isinstance(obj, model.DataSpecificationIEC61360):