I never did see those buttons, are you not confusing with other places? Here is a screenshot of the Timeline panel in CP7:

And this is one from CP9;

I don't see a difference. An important difference for the Timeline panel is the integration of the former Effects panel within it. But no buttons disappeared AFAIK.
If you want to change the stacking order, select an object timeline and drag it up or down.
Maybe you are looking for the Arrange menu? It is still in the right-click menu.
There is also an Align toolbar, which can be opened from the Window menu, and the last four icons can be used as alternative for the Arrange options:
