Remove unused Accounts state (#15611)

* Remove dead state from Accounts

* Refactor to remove reference to self.slot

Account::default() has zero lamports, so would return None anyway

runtime/src/accounts.rs

@@ -19,7 +19,7 @@ use solana_sdk::{
     account::Account,
     account_utils::StateMut,
     bpf_loader_upgradeable::{self, UpgradeableLoaderState},
-    clock::{Epoch, Slot},
+    clock::Slot,
     feature_set::{self, FeatureSet},
     fee_calculator::{FeeCalculator, FeeConfig},
     genesis_config::ClusterType,
@@ -83,12 +83,6 @@ impl AccountLocks {
 /// This structure handles synchronization for db
 #[derive(Default, Debug, AbiExample)]
 pub struct Accounts {
-    /// my slot
-    pub slot: Slot,
-
-    /// my epoch
-    pub epoch: Epoch,
-
     /// Single global AccountsDb
     pub accounts_db: Arc<AccountsDb>,
 
@@ -140,12 +134,10 @@ impl Accounts {
         }
     }
 
-    pub fn new_from_parent(parent: &Accounts, slot: Slot, parent_slot: Slot, epoch: Epoch) -> Self {
+    pub fn new_from_parent(parent: &Accounts, slot: Slot, parent_slot: Slot) -> Self {
         let accounts_db = parent.accounts_db.clone();
         accounts_db.set_hash(slot, parent_slot);
         Self {
-            slot,
-            epoch,
             accounts_db,
             account_locks: Mutex::new(AccountLocks::default()),
         }
@@ -464,10 +456,7 @@ impl Accounts {
 
     /// Slow because lock is held for 1 operation instead of many
     pub fn load_slow(&self, ancestors: &Ancestors, pubkey: &Pubkey) -> Option<(Account, Slot)> {
-        let (account, slot) = self
-            .accounts_db
-            .load_slow(ancestors, pubkey)
-            .unwrap_or((Account::default(), self.slot));
+        let (account, slot) = self.accounts_db.load_slow(ancestors, pubkey)?;
 
         if account.lamports > 0 {
             Some((account, slot))

runtime/src/bank.rs

@@ -980,7 +980,6 @@ impl Bank {
                 &parent.rc.accounts,
                 slot,
                 parent.slot(),
-                epoch,
             )),
             parent: RwLock::new(Some(parent.clone())),
             slot,