message: fix topic error
diff: @@ -43,7 +43,6 @@ mod erc20 {
  from: Option<AccountId>,
  #[ink(topic)]
  to: Option<AccountId>,
  - #[ink(topic)]
  value: Balance,
  }
  @@ -55,7 +54,6 @@ mod erc20 {
  owner: AccountId,
  #[ink(topic)]
  spender: AccountId,
  - #[ink(topic)]
  value: Balance,
  }
  