I made a swap partition to install Ubuntu on my MacBook Air 2011, but now I want to clean all the partitions up. However, I can't delete the "swap partition" in Disk Utility. Can anyone help me?
You should be able to use a tool, such as a GParted Live CD, to delete the swap file partition and resize the OS X partition afterwards.
Per this Apple discussion forum that covered this topic:
Alternately, back up all of your data and applications and wipe/repartition the main drive and install OS X from scratch. Takes a bit longer, but will give you a fresh OS X installation.