message: [ad-hoc filters] Remove legacy split in /explore
diff: @@ -1280,10 +1280,9 @@ class Superset(BaseSupersetView):
  form_data['datasource'] = str(datasource_id) + '__' + datasource_type
  - # On explore, merge extra filters into the form data
  + # On explore, merge legacy and extra filters into the form data
  utils.convert_legacy_filters_into_adhoc(form_data)
  merge_extra_filters(form_data)
  - utils.split_adhoc_filters_into_base_filters(form_data)
  # merge request url params
  if request.method == 'GET':
  