chore: remove weak hashing which does not pull its weight (#10005)

We've had weak/rolling hashing in the code for quite a while. It was a
popular request for a while, based on the belief that rsync does this
and we should too. However, the benefit is quite small; we save on
average about 0.8% of transferred blocks over the population as a whole:

<img width="974" alt="Screenshot 2025-03-28 at 17 09 02"
src="https://github.com/user-attachments/assets/bbe10dea-f85e-4043-9823-7cef1220b4a2"
/>

This would be fine if the cost was comparably low, however the downside
of attempting rolling hash matching is that we (by default) do a
complete file read on the destination in order to look for matches
before we starting pulling blocks for the file. For any larger file this
means a sometimes long, I/O-intensive pause before the file starts
syncing, for usually no benefit.

I propose we simply rip off the bandaid and save the effort.

cmd/dev/stfileinfo/main.go

@@ -72,7 +72,7 @@ func main() {
 		if *standardBlocks || blockSize < protocol.MinBlockSize {
 			blockSize = protocol.BlockSize(fi.Size())
 		}
-		bs, err := scanner.Blocks(context.TODO(), fd, blockSize, fi.Size(), nil, true)
+		bs, err := scanner.Blocks(context.TODO(), fd, blockSize, fi.Size(), nil)
 		if err != nil {
 			log.Fatal(err)
 		}