What does "sunset" mean in this text?

As Waiwai says, "sunset" as a verb means basically "to expire (or run out, shut down, terminate) at its predetermined time." Besides government and laws, you may also hear it in project management; at my current job I was tasked with sunsetting several applications and servers, which meant I had to deal with all the details about taking them out of general use and making sure there were no issues due to them being removed on schedule.

Sunset, in this case, means that those portions of the bill expired. A sunset provision is a special type of clause in a bill that automatically kills certain portions of the bill without requiring the need for it to be repealed. Because this particular use is unique to government, it can generally only be used when referring to laws.

The term, of course, comes from the actual sunset—it ends at a predetermined time.