It only remained on FwupdResult because I couldn't make up my mind about whether
it was a property of the device, or the firmware release. It's more logically
the latter, as you could have a .cab file with multiple versions of the
firmware and only the first being signed.
Although we supported other hashes than SHA1 (which is now moderately unsafe)
we had to switch the metadata provider and daemon on some kind of flag day to
using SHA256. Since that's somewhat impractical, just allow multiple checksums
to be set on objects and just try to match whatever is given in preference
order.
This also means we can easily transition to other hash types in the future.
The removed API was never present in a tarball release, so not an API break.
