There's a closed pull request on the void-packages repository

Switch to bitcoin-core libsecp256k1 and remove libbitcoin; update electrum, Electron-Cash
https://github.com/void-linux/void-packages/pull/43702

Description:
#### Testing the changes
- I tested the changes in this PR: **briefly**

#### New package: libsecp256k1
- This new package conforms to the [package requirements](https://github.com/void-linux/void-packages/blob/master/CONTRIBUTING.md#package-requirements): **YES**

Electrum v4.4.1 moved to using libsecp256k1 0.3.1 (`libsecp256k1.so.2`).

Void's current libsecp256k1 is from https://github.com/libbitcoin/secp256k1, which is extremely outdated.
I believe this was originally used because back then https://github.com/bitcoin-core/secp256k1 was too unstable and did not provide tagged releases. Now they do, so we should move to that.

The only two packages which use libsecp256k1 are `electrum` and `Electron-Cash` (besides the other `libbitcoin-*` packages).

Electron Cash can also use bitcoin-core's libsecp256k1 v0.3.1, although it actually needs https://github.com/Bitcoin-ABC/secp256k1 or Electron Cash's own fork for full functionality (CashFusion would not work):
> you CAN use the Core version, and it will speed-up ECDSA sigs.. but then for Schnorr sigs it won't speed them up at all since Core's Schnorr stuff differs from Bitcoin Cash's. So Electron Cash will detect that it's on Core, and will fall-back to using python-only Schnorr in that case (slow).
> https://github.com/Electron-Cash/Electron-Cash/issues/2596#issuecomment-1529926625

CashFusion is currently not working either since it's already using the wrong version of the library, so switching to bitcoin-core's libsecp256k1 v0.3.1 should be fine for Electron Cash too.

The other 10 libbitcoin packages which also depend on libsecp256k1 have been removed:

- libbitcoin-blockchain
- libbitcoin-client
- libbitcoin-consensus
- libbitcoin-database
- libbitcoin-explorer
- libbitcoin-network
- libbitcoin-node
- libbitcoin-protocol
- libbitcoin-server
- libbitcoin-system