Use Message::from

[tcharding]

In commit 678eee8d7388 Use Message::from_digest we replaced Message::from_digest_slice(hash.as_byte_array()) with Message::from_digest(hash.to_byte_array()) however we failed to notice that we can go one step further because the sighash hash types implement secp256k1::ThirtyTwoByteHash and use Message::from(hash).

[apoelstra]

We definitely did not "fail to notice" this. The use of the ThirtyTwoByteHash trait is the cause of all our "dependency hole" problems related to coordinating rust-bitcoin releases, though I can never remember the exact mechanism of our pain.

[tcharding]

I also forgot what it was exactly, linking to other discussion thread so we talk in one place. rust-bitcoin/rust-secp256k1#673 (comment)

I wrote this issue while trying to remember.