Do I still need to purchase an MPEG-2 and VC-1 license keys for the Raspberry Pi 3?
The point of buying the license keys is to enable hardware decoding of MPEG-2 and VC-1 — see Why does the Raspberry Pi need a MPEG-2 licence? for more information on why you might want this.
While there was much rejoice recently at the patents expiring for MPEG-2, this makes little difference to Pi users, it seems. This thread claims that despite the patents expiring in most countries, the Pi Foundation won't be making any changes until 2025 until all patents are expired across the world.
You can still do software decoding of MPEG-2 without paying any fees, but performance is generally much worse than hardware decoding. If you're creating a media centre and experiencing poor playback of these video files, investing in the license key may be valuable.
So, if you do need hardware decoding for MPEG-2 or VC-1, you still need to pay up, unfortunately, for the foreseeable future, by buying a license key from the store (I might add that I didn't believe that was official until I saw it linked from the official blog!).