They’re still useful. HTTP/2 reduces the impact of some of these practices, but it doesn’t eliminate their impact.
Minification remains as useful as ever. Although HTTP/2 introduces new compression for message headers, that has nothing to do with minification (which is about message bodies). The compression algorithms for message bodies are the same, so minification saves just as much bandwidth as it did before.
Concatenation and sprites will have less of an impact than before, but they will still have some impact. The biggest issue with downloading multiple files instead of a single file with HTTP/1 isn’t actually an HTTP-side problem, per se: there is some bandwidth-based overhead in requesting each file individually, but it’s dwarfed by the time-based overhead of tearing down the TCP/IP session when you’re done with one file, then starting up a new one for the next, and repeating this for every file you want to download.
The biggest focus of HTTP/2 is eliminating that time-based overhead: HTTP/1.1 tried to do this with pipelining, but it didn’t catch on in the browser (Presto is the only engine that got it completely right, and Presto is dead). HTTP/2 is another attempt, which improves on HTTP/1.1’s methods while also making this kind of thing non-optional, and it stands to be more successful. It also eliminates some of the bandwidth-based overhead in making multiple requests, by compressing headers, but it cannot eliminate that overhead completely, and when downloading multiple files, those requests still have to be made (as part of a single TCP/IP session, so there is less overhead, but not zero). So while the impact of concatenating and spriting is proportionally smaller, there is still some impact, especially if you use many files.
Another thing to consider, when it comes to concatenation and spriting, is compression. Concatenated files of similar types tend to compress better than the individual files do, because the compression algorithm can exploit similarities between the concatenated pieces of data. A similar principle applies to sprites: putting similar images in different regions of the same file usually results in a smaller file, because the image’s compression can exploit similarities in the different regions.