Revert "util.get_element_systems to consider all kinds of ifcsystems"

This reverts commit f3f7939c8b.

src/ifcopenshell-python/ifcopenshell/util/system.py

@@ -66,8 +66,13 @@ def get_system_elements(system: ifcopenshell.entity_instance) -> list[ifcopenshe
 def get_element_systems(element: ifcopenshell.entity_instance) -> list[ifcopenshell.entity_instance]:
     results = []
     for rel in element.HasAssignments:
-        if rel.is_a("IfcRelAssignsToGroup") and (group := rel.RelatingGroup).is_a("IfcSystem"):
-            results.append(group)
+        if rel.is_a("IfcRelAssignsToGroup") and rel.RelatingGroup.is_a() in (
+            "IfcSystem",
+            "IfcDistributionSystem",
+            "IfcBuildingSystem",
+            "IfcZone",
+        ):
+            results.append(rel.RelatingGroup)
     return results