Support multiple BLS implementations (#1335)

## Issue Addressed

NA

## Proposed Changes

- Refactor the `bls` crate to support multiple BLS "backends" (e.g., milagro, blst, etc).
- Removes some duplicate, unused code in `common/rest_types/src/validator.rs`.
- Removes the old "upgrade legacy keypairs" functionality (these were unencrypted keys that haven't been supported for a few testnets, no one should be using them anymore).

## Additional Info

Most of the files changed are just inconsequential changes to function names.

## TODO

- [x] Optimization levels
- [x] Infinity point: https://github.com/supranational/blst/issues/11
- [x] Ensure milagro *and* blst are tested via CI
- [x] What to do with unsafe code?
- [x] Test infinity point in signature sets

lighthouse/tests/account_manager.rs

@@ -1,7 +1,6 @@
 #![cfg(not(debug_assertions))]
 
 use account_manager::{
-    upgrade_legacy_keypairs::{CMD as UPGRADE_CMD, *},
     validator::{create::*, CMD as VALIDATOR_CMD},
     wallet::{
         create::{CMD as CREATE_CMD, *},
@@ -16,7 +15,6 @@ use std::path::{Path, PathBuf};
 use std::process::{Command, Output};
 use std::str::from_utf8;
 use tempfile::{tempdir, TempDir};
-use types::Keypair;
 use validator_dir::ValidatorDir;
 
 // TODO: create tests for the `lighthouse account validator deposit` command. This involves getting
@@ -365,56 +363,3 @@ fn validator_create() {
 
     assert_eq!(dir_child_count(validator_dir.path()), 6);
 }
-
-fn write_legacy_keypair<P: AsRef<Path>>(name: &str, dir: P) -> Keypair {
-    let keypair = Keypair::random();
-
-    let mut keypair_bytes = keypair.pk.as_bytes().to_vec();
-    keypair_bytes.extend_from_slice(keypair.sk.as_bytes().as_ref());
-
-    fs::write(dir.as_ref().join(name), &keypair_bytes).unwrap();
-
-    keypair
-}
-
-#[test]
-fn upgrade_legacy_keypairs() {
-    let validators_dir = tempdir().unwrap();
-    let secrets_dir = tempdir().unwrap();
-
-    let validators = (0..2)
-        .into_iter()
-        .map(|i| {
-            let validator_dir = validators_dir.path().join(format!("myval{}", i));
-
-            fs::create_dir_all(&validator_dir).unwrap();
-
-            let voting_keypair = write_legacy_keypair(VOTING_KEYPAIR_FILE, &validator_dir);
-            let withdrawal_keypair = write_legacy_keypair(WITHDRAWAL_KEYPAIR_FILE, &validator_dir);
-
-            (validator_dir, voting_keypair, withdrawal_keypair)
-        })
-        .collect::<Vec<_>>();
-
-    account_cmd()
-        .arg(UPGRADE_CMD)
-        .arg(format!("--{}", VALIDATOR_DIR_FLAG))
-        .arg(validators_dir.path().as_os_str())
-        .arg(format!("--{}", SECRETS_DIR_FLAG))
-        .arg(secrets_dir.path().as_os_str())
-        .output()
-        .unwrap();
-
-    for (validator_dir, voting_keypair, withdrawal_keypair) in validators {
-        let dir = ValidatorDir::open(&validator_dir).unwrap();
-
-        assert_eq!(
-            voting_keypair.pk,
-            dir.voting_keypair(secrets_dir.path()).unwrap().pk
-        );
-        assert_eq!(
-            withdrawal_keypair.pk,
-            dir.withdrawal_keypair(secrets_dir.path()).unwrap().pk
-        );
-    }
-}