How do I remove aluminum foil from the bottom of my oven?
That looks a lot like melted aluminum.

I'd use a solution of sodium hydroxide to dissolve it; probably won't even hurt the oven paint.

Easy Off Heavy Duty Oven Cleaner is NaOH based, so that'll probably work for you, and is easier to find than straight lye nowadays.
Just follow the directions. If the aluminum is thick, you may have to do things twice. 

Other brands of oven cleaner will likely work as well as long as they contain sodium hydroxide (lye). It will help A LOT for you people who need aluminum foil off your oven!