Signature checks do not require arrays of signers

The requestWithdrawal, modifyLocker, and emergencyUnlock functions accept a signers array. This is passed into checkValidatorSignatures to verify that the action is authorized:

function checkValidatorSignatures(
  bytes32 message,
  ValidatorSet memory activeValidatorSet, // Active set of all L1 validators
  address[] memory signers, // Subsequence of the active L1 validators that signed the message
  Signature[] memory signatures,
  bytes32 validatorSetHash
) private view {

The array of signers is not necessary for performing the validator check. Instead, checkValidatorSignatures could simply recover the array of signers and check that it is a sufficiently weighted subsequence of the chosen validator set. Omitting this argument from these external functions would simplify the interface and save gas.

Note: this issue was addressed in commit ; the signers array is no longer required to be provided by the user, and the signer's address recovered from the individual signatures is used instead.