Check if we can move off forked deps

[elsirion]

Some of the changes MiniMint needs have landed upstream by now, check if we can get rid of some of our forks of:

• rust-secp256k1[-zkp]
• bitcoin_hashes

[justinmoon]

I attempted this and failed.

• secp256k1_zkp still needs to merge https://github.com/ElementsProject/rust-secp256k1-zkp/pull/48
• bitcoin_hashes needs to release another version containing https://github.com/rust-bitcoin/bitcoin_hashes/commit/f1084bf63b518f76d1f77abe7709ceabd4ef65ee

Pushed my incomplete changes to a branch

[dpc]

Closing as done long time ago.