Remove unused struct field

contracts/staking/contracts/src/interfaces/IStructs.sol

@@ -53,12 +53,10 @@ interface IStructs {
     /// Note that these balances may be stale if the current epoch
     /// is greater than `currentEpoch`.
     /// Always load this struct using _loadSyncedBalance or _loadUnsyncedBalance.
-    /// @param isInitialized
     /// @param currentEpoch the current epoch
     /// @param currentEpochBalance balance in the current epoch.
     /// @param nextEpochBalance balance in `currentEpoch+1`.
     struct StoredBalance {
-        bool isInitialized;
         uint32 currentEpoch;
         uint96 currentEpochBalance;
         uint96 nextEpochBalance;

contracts/staking/contracts/src/stake/MixinStakeStorage.sol

@@ -177,7 +177,6 @@ contract MixinStakeStorage is
     {
         // note - this compresses into a single `sstore` when optimizations are enabled,
         // since the StakeBalance struct occupies a single word of storage.
-        balancePtr.isInitialized = true;
         balancePtr.currentEpoch = balance.currentEpoch;
         balancePtr.nextEpochBalance = balance.nextEpochBalance;
         balancePtr.currentEpochBalance = balance.currentEpochBalance;

contracts/staking/contracts/test/TestDelegatorRewards.sol

@@ -117,7 +117,6 @@ contract TestDelegatorRewards is
             delegator
         );
         IStructs.StoredBalance storage _stake = _delegatedStakeToPoolByOwner[delegator][poolId];
-        _stake.isInitialized = true;
         _stake.currentEpochBalance += uint96(stake);
         _stake.nextEpochBalance += uint96(stake);
         _stake.currentEpoch = uint32(currentEpoch);
@@ -146,7 +145,6 @@ contract TestDelegatorRewards is
         if (_stake.currentEpoch < currentEpoch) {
             _stake.currentEpochBalance = _stake.nextEpochBalance;
         }
-        _stake.isInitialized = true;
         _stake.nextEpochBalance += uint96(stake);
         _stake.currentEpoch = uint32(currentEpoch);
     }
@@ -170,7 +168,6 @@ contract TestDelegatorRewards is
         if (_stake.currentEpoch < currentEpoch) {
             _stake.currentEpochBalance = _stake.nextEpochBalance;
         }
-        _stake.isInitialized = true;
         _stake.nextEpochBalance -= uint96(stake);
         _stake.currentEpoch = uint32(currentEpoch);
     }

contracts/staking/test/unit_tests/mixin_stake_storage_test.ts

@@ -26,19 +26,16 @@ blockchainTests.resets('MixinStakeStorage unit tests', env => {
         );
         await testContract.setCurrentEpoch.awaitTransactionSuccessAsync(CURRENT_EPOCH);
         defaultUninitializedBalance = {
-            isInitialized: false,
             currentEpoch: constants.INITIAL_EPOCH,
             currentEpochBalance: new BigNumber(0),
             nextEpochBalance: new BigNumber(0),
         };
         defaultSyncedBalance = {
-            isInitialized: true,
             currentEpoch: CURRENT_EPOCH,
             currentEpochBalance: new BigNumber(16),
             nextEpochBalance: new BigNumber(16),
         };
         defaultUnsyncedBalance = {
-            isInitialized: true,
             currentEpoch: CURRENT_EPOCH.minus(1),
             currentEpochBalance: new BigNumber(10),
             nextEpochBalance: new BigNumber(16),
@@ -48,7 +45,6 @@ blockchainTests.resets('MixinStakeStorage unit tests', env => {
     async function getTestBalancesAsync(index: Numberish): Promise<StoredBalance> {
         const storedBalance: Partial<StoredBalance> = {};
         [
-            storedBalance.isInitialized,
             storedBalance.currentEpoch,
             storedBalance.currentEpochBalance,
             storedBalance.nextEpochBalance,

contracts/staking/test/utils/types.ts

@@ -59,7 +59,6 @@ export interface EndOfEpochInfo {
 }
 
 export interface StoredBalance {
-    isInitialized: boolean;
     currentEpoch: number | BigNumber;
     currentEpochBalance: BigNumber;
     nextEpochBalance: BigNumber;