This reverts commit 100e7cc337.
Unlike the last version, this fixes `--print-out-paths` for old clients
When the client lacks `featureRealisationWithPath` (worker) or version <
2.8 (serve), the daemon was sending an empty `StringMap` for
`builtOutputs`, causing `--print-out-paths` to print nothing. This
commit constructs the old wire format instead, using a dummy `sha256:`
hash since the derivation hash no longer exists. Old clients only need
the output name and path from the JSON.
faca7db633