Remove block_root_tree reminents

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -187,7 +187,6 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             genesis_block_root: self.genesis_block_root,
             ssz_head_tracker: self.head_tracker.to_ssz_container(),
             fork_choice: self.fork_choice.as_ssz_container(),
-            block_root_tree: vec![],
             eth1_cache: self.eth1_chain.as_ref().map(|x| x.as_ssz_container()),
         };
 

beacon_node/beacon_chain/src/persisted_beacon_chain.rs

@@ -19,8 +19,6 @@ pub struct PersistedBeaconChain<T: BeaconChainTypes> {
     pub genesis_block_root: Hash256,
     pub ssz_head_tracker: SszHeadTracker,
     pub fork_choice: SszForkChoice,
-    // TODO: remove this.
-    pub block_root_tree: Vec<u8>,
     pub eth1_cache: Option<SszEth1>,
 }