Cannot open metadata detail with thesaurus

[mattiagiupponi]

Expected Behavior

Open the metadata editor with some thesaurus installed should work

Actual Behavior

The page raises an issue since the method remove_country_from_languagecode is declared as a static method.
Probably a regression of this issue #9799 since it was introduced here

Internal Server Error: /datasets/geonode_data:geonode:malga_70f2ed645b1b775f20a9a20e875f9dfb/metadata
Traceback (most recent call last):
  File "/home/mattia/.virtualenvs/metamedia/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/mattia/.virtualenvs/metamedia/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/mattia/.virtualenvs/metamedia/lib/python3.8/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/opt/core/geonode/geonode/decorators.py", line 213, in _inner
    return function(request, *args, **kwargs)
  File "/opt/core/geonode/geonode/layers/views.py", line 590, in dataset_metadata
    tkeywords_form = ThesaurusAvailableForm(prefix='tkeywords')
  File "/opt/core/geonode/geonode/base/forms.py", line 314, in __init__
    self.fields[f"{item.id}"] = self._define_multifield(item, False, tname, lang)
  File "/opt/core/geonode/geonode/base/forms.py", line 330, in _define_multifield
    choices=self._get_thesauro_keyword_label(item, lang),
  File "/opt/core/geonode/geonode/base/forms.py", line 354, in _get_thesauro_keyword_label
    lang = remove_country_from_lanugecode(lang)
TypeError: 'staticmethod' object is not callable

Steps to Reproduce the Problem

1. Load a thesaurus in geonode
2. open the metadata editor

Specifications

• GeoNode version: master, 4.x
• Installation method (manual, GeoNode Docker, SPCGeoNode Docker): all
• Platform: all
• Additional details:

FYI: @mwallschlaeger