Remove fallback support from eth1 service (#3594)

## Issue Addressed

N/A

## Proposed Changes

With https://github.com/sigp/lighthouse/pull/3214 we made it such that you can either have 1 auth endpoint or multiple non auth endpoints. Now that we are post merge on all networks (testnets and mainnet), we cannot progress a chain without a dedicated auth execution layer connection so there is no point in having a non-auth eth1-endpoint for syncing deposit cache. 

This code removes all fallback related code in the eth1 service. We still keep the single non-auth endpoint since it's useful for testing.

## Additional Info

This removes all eth1 fallback related metrics that were relevant for the monitoring service, so we might need to change the api upstream.

beacon_node/genesis/src/eth1_genesis_service.rs

@@ -43,7 +43,7 @@ impl Eth1GenesisService {
     /// Creates a new service. Does not attempt to connect to the Eth1 node.
     ///
     /// Modifies the given `config` to make it more suitable to the task of listening to genesis.
-    pub fn new(config: Eth1Config, log: Logger, spec: ChainSpec) -> Self {
+    pub fn new(config: Eth1Config, log: Logger, spec: ChainSpec) -> Result<Self, String> {
         let config = Eth1Config {
             // Truncating the block cache makes searching for genesis more
             // complicated.
@@ -64,15 +64,16 @@ impl Eth1GenesisService {
             ..config
         };
 
-        Self {
-            eth1_service: Eth1Service::new(config, log, spec),
+        Ok(Self {
+            eth1_service: Eth1Service::new(config, log, spec)
+                .map_err(|e| format!("Failed to create eth1 service: {:?}", e))?,
             stats: Arc::new(Statistics {
                 highest_processed_block: AtomicU64::new(0),
                 active_validator_count: AtomicUsize::new(0),
                 total_deposit_count: AtomicUsize::new(0),
                 latest_timestamp: AtomicU64::new(0),
             }),
-        }
+        })
     }
 
     /// Returns the first eth1 block that has enough deposits that it's a (potentially invalid)
@@ -112,11 +113,9 @@ impl Eth1GenesisService {
             "Importing eth1 deposit logs";
         );
 
-        let endpoints = eth1_service.init_endpoints()?;
-
         loop {
             let update_result = eth1_service
-                .update_deposit_cache(None, &endpoints)
+                .update_deposit_cache(None)
                 .await
                 .map_err(|e| format!("{:?}", e));
 
@@ -158,7 +157,7 @@ impl Eth1GenesisService {
             }
 
             // Download new eth1 blocks into the cache.
-            let blocks_imported = match eth1_service.update_block_cache(None, &endpoints).await {
+            let blocks_imported = match eth1_service.update_block_cache(None).await {
                 Ok(outcome) => {
                     debug!(
                         log,

beacon_node/genesis/tests/tests.rs

@@ -44,10 +44,9 @@ fn basic() {
 
         let service = Eth1GenesisService::new(
             Eth1Config {
-                endpoints: Eth1Endpoint::NoAuth(vec![SensitiveUrl::parse(
-                    eth1.endpoint().as_str(),
-                )
-                .unwrap()]),
+                endpoint: Eth1Endpoint::NoAuth(
+                    SensitiveUrl::parse(eth1.endpoint().as_str()).unwrap(),
+                ),
                 deposit_contract_address: deposit_contract.address(),
                 deposit_contract_deploy_block: now,
                 lowest_cached_block_number: now,
@@ -57,7 +56,8 @@ fn basic() {
             },
             log,
             spec.clone(),
-        );
+        )
+        .unwrap();
 
         // NOTE: this test is sensitive to the response speed of the external web3 server. If
         // you're experiencing failures, try increasing the update_interval.