message: [Secure Storage] Remove "unimplemented!()" as default implementation from CryptoStorage.
  Closes:
diff: @@ -21,9 +21,7 @@ pub trait CryptoStorage {
  /// not used correctly. As this is purely a testing API, there is no defined behavior for
  /// importing a key for a given name if that name already exists. It only exists to allow
  /// Libra to be run in test environments where a set of deterministic keys must be generated.
  - fn import_private_key(&mut self, _name: &str, _key: Ed25519PrivateKey) -> Result<(), Error> {
  - unimplemented!();
  - }
  + fn import_private_key(&mut self, _name: &str, _key: Ed25519PrivateKey) -> Result<(), Error>;
  /// Returns the Ed25519 private key stored at 'name' and identified by 'version', which is the
  /// corresponding public key. This may fail even if the 'named' key exists but the version is
  