engine error: remove faulty/unused From

ethcore/types/src/errors/engine_error.rs

@@ -16,12 +16,11 @@
 
 use std::fmt;
 
-use derive_more::From;
 use ethereum_types::{Address, H64, H256};
 use unexpected::{Mismatch, OutOfBounds};
 
 /// Voting errors.
-#[derive(Debug, From)]
+#[derive(Debug)]
 pub enum EngineError {
  /// Signature or author field does not belong to an authority.
  NotAuthorized(Address),
@@ -78,11 +77,11 @@ impl fmt::Display for EngineError {
  use self::EngineError::*;
  let msg = match *self {
  CliqueMissingCheckpoint(ref hash) => format!("Missing checkpoint block: {}", hash),
- CliqueMissingVanity => format!("Extra data is missing vanity data"),
- CliqueMissingSignature => format!("Extra data is missing signature"),
+ CliqueMissingVanity => "Extra data is missing vanity data".into(),
+ CliqueMissingSignature => "Extra data is missing signature".into(),
  CliqueCheckpointInvalidSigners(len) => format!("Checkpoint block list was of length: {} of checkpoint but
  it needs to be bigger than zero and a divisible by 20", len),
- CliqueCheckpointNoSigner => format!("Checkpoint block list of signers was empty"),
+ CliqueCheckpointNoSigner => "Checkpoint block list of signers was empty".into(),
  CliqueInvalidNonce(ref mis) => format!("Unexpected nonce {} expected {} or {}", mis, 0_u64, u64::max_value()),
  CliqueWrongAuthorCheckpoint(ref oob) => format!("Unexpected checkpoint author: {}", oob),
  CliqueFaultyRecoveredSigners(ref mis) => format!("Faulty recovered signers {:?}", mis),
@@ -98,9 +97,9 @@ impl fmt::Display for EngineError {
  SystemCallResultDecoding(ref msg) => format!("Failed to decode the result of a system call: {}", msg),
  SystemCallResultInvalid(ref msg) => format!("The result of a system call is invalid: {}", msg),
  MalformedMessage(ref msg) => format!("Received malformed consensus message: {}", msg),
- RequiresClient => format!("Call requires client but none registered"),
- RequiresSigner => format!("Call requires signer but none registered"),
- InvalidEngine => format!("Invalid engine specification or implementation"),
+ RequiresClient => "Call requires client but none registered".into(),
+ RequiresSigner => "Call requires signer but none registered".into(),
+ InvalidEngine => "Invalid engine specification or implementation".into(),
  MissingParent(ref hash) => format!("Parent Epoch is missing from database: {}", hash),
  };