Deprecate eth1 and dummy-eth1 flags (#6566)

* Deprecate eth1/dummy-eth1 flags

* Update book

* Simplify + make staking conflict with disable-deposit-contract

lighthouse/tests/beacon_node.rs

@@ -396,13 +396,14 @@ fn genesis_backfill_with_historic_flag() {
 }
 
 // Tests for Eth1 flags.
+// DEPRECATED but should not crash
 #[test]
 fn dummy_eth1_flag() {
     CommandLineTest::new()
         .flag("dummy-eth1", None)
-        .run_with_zero_port()
-        .with_config(|config| assert!(config.dummy_eth1_backend));
+        .run_with_zero_port();
 }
+// DEPRECATED but should not crash
 #[test]
 fn eth1_flag() {
     CommandLineTest::new()
@@ -2483,6 +2484,21 @@ fn sync_eth1_chain_disable_deposit_contract_sync_flag() {
         .with_config(|config| assert_eq!(config.sync_eth1_chain, false));
 }
 
+#[test]
+#[should_panic]
+fn disable_deposit_contract_sync_conflicts_with_staking() {
+    let dir = TempDir::new().expect("Unable to create temporary directory");
+    CommandLineTest::new_with_no_execution_endpoint()
+        .flag("disable-deposit-contract-sync", None)
+        .flag("staking", None)
+        .flag("execution-endpoints", Some("http://localhost:8551/"))
+        .flag(
+            "execution-jwt",
+            dir.path().join("jwt-file").as_os_str().to_str(),
+        )
+        .run_with_zero_port();
+}
+
 #[test]
 fn light_client_server_default() {
     CommandLineTest::new()