[Types] Fix warning
[Types] Fix warning

```
   Compiling types v0.1.0 (/Users/wqfish/github/libra/types)
warning: unused import: `crypto::HashValue`
  --> types/src/account_config.rs:19:5
   |
19 | use crypto::HashValue;
   |     ^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(unused_imports)] on by default
```

aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core