message: [examples/erc20] Some minor code clean-up
diff: @@ -6,12 +6,10 @@ use pdsl_core::{
  Key,
  alloc::ForwardAlloc,
  },
  - env::{Env, ContractEnv, srml::Address},
  + env::{Env, ContractEnv, srml::Address, srml::Balance},
  };
  use parity_codec::{Encode, Decode};
  -type Balance = u64;
  -
  /// Returns the zero address.
  fn zero_address() -> Address {
  Address::from([0x0_u8; 32].as_ref())
  @@ -30,8 +28,6 @@ pub struct Erc20Token {
  allowances: storage::HashMap<(Address, Address), Balance>,
  /// The total supply.
  total_supply: storage::Value<Balance>,
  - /// The allocator for newly allocated entities.
  - alloc: storage::alloc::CellChunkAlloc,
  }
  impl Erc20Token {
  @@ -108,7 +104,6 @@ impl Erc20Token {
  balances: storage::HashMap::new_using_alloc(alloc),
  allowances: storage::HashMap::new_using_alloc(alloc),
  total_supply: storage::Value::new_using_alloc(alloc, 0),
  - alloc: storage::alloc::CellChunkAlloc::new_using_alloc(alloc),
  }
  }
  }
  