Remove legacy max-skip-slots checks (sigp#4403)

Remove `max-skip-slots` checks when processing blocks.
This was legacy code which was previously used in the Medalla testnet to sync to the correct fork.
With the addition of checkpoint sync which allows us to sync to any arbitrary fork, this is no longer a necessary feature, so it has been removed for simplicity.

The CLI flag and checks for attestation processing have been retained as it still may have uses in DoS protection.

Author: macladson

beacon_node/beacon_chain/src/chain_config.rs

@@ -17,8 +17,7 @@ pub const FORK_CHOICE_LOOKAHEAD_FACTOR: u32 = 24;
 
 #[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize)]
 pub struct ChainConfig {
-    /// Maximum number of slots to skip when importing a consensus message (e.g., block,
-    /// attestation, etc).
+    /// Maximum number of slots to skip when importing an attestation.
     ///
     /// If `None`, there is no limit.
     pub import_max_skip_slots: Option<u64>,

beacon_node/network/src/beacon_processor/worker/gossip_methods.rs

@@ -830,7 +830,6 @@ impl<T: BeaconChainTypes> Worker<T> {
             | Err(e @ BlockError::NonLinearParentRoots)
             | Err(e @ BlockError::BlockIsNotLaterThanParent { .. })
             | Err(e @ BlockError::InvalidSignature)
-            | Err(e @ BlockError::TooManySkippedSlots { .. })
             | Err(e @ BlockError::WeakSubjectivityConflict)
             | Err(e @ BlockError::InconsistentFork(_))
             | Err(e @ BlockError::ExecutionPayloadError(_))

beacon_node/src/cli.rs

@@ -727,7 +727,7 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
             Arg::with_name("max-skip-slots")
                 .long("max-skip-slots")
                 .help(
-                    "Refuse to skip more than this many slots when processing a block or attestation. \
+                    "Refuse to skip more than this many slots when processing an attestation. \
                     This prevents nodes on minority forks from wasting our time and disk space, \
                     but could also cause unnecessary consensus failures, so is disabled by default."
                 )