Revert "Reuse milhouse subtrees to shrink inactivity_scores in memory (#7062)"

This reverts commit 6399ad482b.

beacon_node/beacon_chain/src/test_utils.rs

@@ -2713,16 +2713,16 @@ where
         let mut block_hash_from_slot: HashMap<Slot, SignedBeaconBlockHash> = HashMap::new();
         let mut state_hash_from_slot: HashMap<Slot, BeaconStateHash> = HashMap::new();
         for slot in slots {
-            // Using a `Box::pin` to reduce the stack size. Clippy was raising a lints.
-            let (block_hash, new_state) = Box::pin(self.add_attested_block_at_slot_with_sync(
-                *slot,
-                state,
-                state_root,
-                validators,
-                sync_committee_strategy,
-            ))
-            .await
-            .unwrap();
+            let (block_hash, new_state) = self
+                .add_attested_block_at_slot_with_sync(
+                    *slot,
+                    state,
+                    state_root,
+                    validators,
+                    sync_committee_strategy,
+                )
+                .await
+                .unwrap();
 
             state = new_state;