Feature gate withdrawals (#3684)

* start feature gating

* feature gate withdrawals

beacon_node/beacon_chain/Cargo.toml

@@ -10,6 +10,8 @@ default = ["participation_metrics"]
 write_ssz_files = []  # Writes debugging .ssz files to /tmp during block processing.
 participation_metrics = []  # Exposes validator participation metrics to Prometheus.
 fork_from_env = [] # Initialise the harness chain spec from the FORK_NAME env variable
+withdrawals = ["state_processing/withdrawals", "types/withdrawals", "store/withdrawals", "execution_layer/withdrawals"]
+withdrawals-processing = ["state_processing/withdrawals-processing", "store/withdrawals-processing", "execution_layer/withdrawals-processing"]
 
 [dev-dependencies]
 maplit = "1.0.2"

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -4117,6 +4117,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                     .get_suggested_fee_recipient(proposer as u64)
                     .await,
                 //FIXME(sean)
+                #[cfg(feature = "withdrawals")]
                 withdrawals: vec![],
             }),
         };