Clean up `daemonImageDestination.PutBlob` digest handling

[mtrmac]

See #193 (comment) .

[rhatdan]

@mtrmac @vrothberg What is the state of this issue. It is two years old, can we close it?

[mtrmac]

This was actually fixed in #370: We now always use the same digest for the path and for the data returned from PutBlob.