Cullface no longer works for the top faces of potted cactus and bamboo

Likely from the fix to MC-195461.

Despite cullface=up being clearly defined for these elements in both of these blocks' model json files, it is not executed, resulting in the faces being rendered at all times even when completely obscured and not visible.

No idea how this happened - almost all other blocks with upwards cullface (e.g. fences, full solid cubes) correctly render that face when an upper slab is above them, but cull it when that face is fully obscured.