SQLCatalog._getColumnIds: Merge into only caller.

Callers up the stack should not mutate returned value (and all callers
found in this repository code follow this rule).
Saves a list copy and an extra call on each call, and a few lines of code.

product/ZSQLCatalog/SQLCatalog.py

@@ -1112,8 +1112,13 @@ class Catalog(Folder,
     """
     return self._getCatalogSchema()[table]
 
+  security.declarePrivate('getColumnIds')
   @transactional_cache_decorator('SQLCatalog.getColumnIds')
-  def _getColumnIds(self):
+  def getColumnIds(self):
+    """
+    Calls the show column method and returns dictionnary of
+    Field Ids
+    """
     keys = set()
     add_key = keys.add
     table_dict = self._getCatalogSchema()
@@ -1129,14 +1134,6 @@ class Catalog(Folder,
       add_key(scriptable_tuple[0].strip())
     return sorted(keys)
 
-  security.declarePrivate('getColumnIds')
-  def getColumnIds(self):
-    """
-    Calls the show column method and returns dictionnary of
-    Field Ids
-    """
-    return self._getColumnIds()[:]
-
   security.declarePrivate('getColumnMap')
   @transactional_cache_decorator('SQLCatalog.getColumnMap')
   def getColumnMap(self):