Altair consensus changes and refactors (#2279)

## Proposed Changes

Implement the consensus changes necessary for the upcoming Altair hard fork.

## Additional Info

This is quite a heavy refactor, with pivotal types like the `BeaconState` and `BeaconBlock` changing from structs to enums. This ripples through the whole codebase with field accesses changing to methods, e.g. `state.slot` => `state.slot()`.


Co-authored-by: realbigsean <seananderson33@gmail.com>

lighthouse/src/main.rs

@@ -18,8 +18,6 @@ use task_executor::ShutdownReason;
 use types::{EthSpec, EthSpecId};
 use validator_client::ProductionValidatorClient;
 
-pub const ETH2_CONFIG_FILENAME: &str = "eth2-spec.toml";
-
 fn bls_library_name() -> &'static str {
     if cfg!(feature = "portable") {
         "blst-portable"
@@ -125,7 +123,7 @@ fn main() {
                 .long("network")
                 .value_name("network")
                 .help("Name of the Eth2 chain Lighthouse will sync and follow.")
-                .possible_values(&["medalla", "altona", "spadina", "pyrmont", "mainnet", "toledo", "prater"])
+                .possible_values(&["pyrmont", "mainnet", "prater"])
                 .conflicts_with("testnet-dir")
                 .takes_value(true)
                 .global(true)
@@ -207,11 +205,7 @@ fn main() {
             EthSpecId::Mainnet => run(EnvironmentBuilder::mainnet(), &matches, testnet_config),
             #[cfg(feature = "spec-minimal")]
             EthSpecId::Minimal => run(EnvironmentBuilder::minimal(), &matches, testnet_config),
-            #[cfg(feature = "spec-v12")]
-            EthSpecId::V012Legacy => {
-                run(EnvironmentBuilder::v012_legacy(), &matches, testnet_config)
-            }
-            #[cfg(any(not(feature = "spec-minimal"), not(feature = "spec-v12")))]
+            #[cfg(any(not(feature = "spec-minimal")))]
             other => {
                 eprintln!(
                     "Eth spec `{}` is not supported by this build of Lighthouse",