remove unused func

Author: rmorshea

src/idom/core/_f_back.py

@@ -7,7 +7,7 @@
 def f_module_name(index: int = 0) -> str:
     frame = f_back(index + 1)
     if frame is None:
-        return ""
+        return ""  # pragma: no cover
     name = frame.f_globals.get("__name__", "")
     assert isinstance(name, str), "Expected module name to be a string"
     return name
@@ -20,4 +20,4 @@ def f_back(index: int = 0) -> FrameType | None:
             return frame
         frame = frame.f_back
         index -= 1
-    return None
+    return None  # pragma: no cover

src/idom/core/layout.py

@@ -481,12 +481,6 @@ def _check_should_render(old: ComponentType, new: ComponentType) -> bool:
         return False
 
 
-def _iter_model_state_children(model_state: _ModelState) -> Iterator[_ModelState]:
-    yield model_state
-    for child in model_state.children_by_key.values():
-        yield from _iter_model_state_children(child)
-
-
 def _new_root_model_state(
     component: ComponentType, schedule_render: Callable[[_LifeCycleStateId], None]
 ) -> _ModelState: