I'd just like to point out something:
Maybe this law isn't as useless as you think. What if the next president would like to kill US citizens with drones. Or the next one. Or maybe Obama changes his mind. Laws are supposed to be a limit, list of things we don't want people to do. There are laws against murder although most people go trhough their whole lives without murdering anyone.
Besides: Laws and goverment powers should not be based on who happens to be in power at the time. For example: I don't think president Niinistö would start executing people if he doesn't like their hair BUT I would not want the parliament to make a law saying "President can sentence people to death if their hair looks bad." Simply saying, "it's cool, I know that this president would not misuse that law" is not a good defense because we don't know who will be the next president.
Very silly example, I know.
In the case of Obama and the drones, Obama has used the drones to kill citizens of USA. This was according to the laws of USA and within his powers as a president. Making a law limiting that power to does not seem like a bad idea.
I do admit that this is not the most important thing for your country right now but it doesn't mean that it should not be done either.