fd86f998f Squashed 'src/secp256k1/' changes from 84973d393..0b7024185 (MarcoFalke)
Pull request description:
The subtree should now match upstream again. Check with:
```sh
./contrib/devtools/git-subtree-check.sh src/secp256k1
```
The changes are only documentation/refactoring related.
Tree-SHA512: 43e8a95bcbfefef9e19ec38a92d2d57fdd4a16ddf726e036d36a0d806eb6f35b45b40ee69f980430e107895ec8725b5de4e36456b026214675e0b19630bb6fe9