Simplify code, avoid docstring rot

convert.py

@@ -159,25 +159,12 @@ def load_series_xml_file(xml_file: Path):
             if k != "TIME_PERIOD" and k != "OBS_VALUE" and v != ""
         }
 
-    NON_WANTED_SERIES_ATTRIBUTES = {
-        "FREQ",
-        "BBK_ID",
-        "BBK_TITLE",
-        "BBK_TITLE_ENG",
-        "BBK_COMM_GEN",
-        "BBK_COMM_GEN_ENG",
-    }
-
     def compute_series_attributes(elt):
-        """Compute a dictionary containing additional information about series.
-
-        This applies to series other than FREQ, BBK_ID, BBK_TITLE*, BBK_COMM_GEN
-        and BBK_COMM_GEN_ENG
-        """
+        """Compute a dictionary containing additional information about series."""
         return {
             k: norm_space(v)
             for k, v in elt.attrib.items()
-            if k not in NON_WANTED_SERIES_ATTRIBUTES and v != ""
+            if k not in {"FREQ", "BBK_TITLE", "BBK_TITLE_ENG", "BBK_COMM_GEN", "BBK_COMM_GEN_ENG"} and v != ""
         }
 
     SERIES_TAG = "{http://www.bundesbank.de/statistik/zeitreihen/BBKcompact}Series"