Update Solana to a more recent version

[ruuda]

At the moment we use the Solana 1.7.8 SDK, because Anchor the eDSL demands this version, and the Serum multisig program uses Anchor. It would be good to update to a more recent version, especially so we can drop our patches from the [patch.crates-io] section in Cargo.toml, as those changes have been merged upstream.