Really hashing a random hash is not necessary

[RCasatta]

https://github.com/0xtlt/nostr_rust/blob/b8a9ab72c0f46627ceec37f2ca5a763d55626a89/src/utils.rs#L29

A hash where the preimage is unknown is indistinguishable from random, so hashing is not necessary, just return 32 random bytes.