Remove SignatureBouncer contract

(cherry picked from commit c8762544)

contracts/drafts/SignatureBouncer.sol

-pragma solidity ^0.5.0;
-
-import "../GSN/Context.sol";
-import "../access/roles/SignerRole.sol";
-import "../cryptography/ECDSA.sol";
-
-/**
- * @title SignatureBouncer
- * @author PhABC, Shrugs and aflesher
- * @dev SignatureBouncer allows users to submit a signature as a permission to
- * do an action.
- * If the signature is from one of the authorized signer addresses, the
- * signature is valid.
- * Note that SignatureBouncer offers no protection against replay attacks, users
- * must add this themselves!
- *
- * Signer addresses can be individual servers signing grants or different
- * users within a decentralized club that have permission to invite other
- * members. This technique is useful for whitelists and airdrops; instead of
- * putting all valid addresses on-chain, simply sign a grant of the form
- * keccak256(abi.encodePacked(`:contractAddress` + `:granteeAddress`)) using a
- * valid signer address.
- * Then restrict access to your crowdsale/whitelist/airdrop using the
- * `onlyValidSignature` modifier (or implement your own using _isValidSignature).
- * In addition to `onlyValidSignature`, `onlyValidSignatureAndMethod` and
- * `onlyValidSignatureAndData` can be used to restrict access to only a given
- * method or a given method with given parameters respectively.
- * See the tests in SignatureBouncer.test.js for specific usage examples.
- *
- * @notice A method that uses the `onlyValidSignatureAndData` modifier must make
- * the _signature parameter the "last" parameter. You cannot sign a message that
- * has its own signature in it so the last 128 bytes of msg.data (which
- * represents the length of the _signature data and the _signature data itself)
- * is ignored when validating. Also non fixed sized parameters make constructing
- * the data in the signature much more complex.
- * See https://ethereum.stackexchange.com/a/50616 for more details.
- */
-contract SignatureBouncer is Context, SignerRole {
-    using ECDSA for bytes32;
-
-    // Function selectors are 4 bytes long, as documented in
-    // https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector
-    uint256 private constant _METHOD_ID_SIZE = 4;
-    // Signature size is 65 bytes (tightly packed v + r + s), but gets padded to 96 bytes
-    uint256 private constant _SIGNATURE_SIZE = 96;
-
-    constructor () internal {
-        // solhint-disable-previous-line no-empty-blocks
-    }
-
-    /**
-     * @dev Requires that a valid signature of a signer was provided.
-     */
-    modifier onlyValidSignature(bytes memory signature) {
-        require(_isValidSignature(_msgSender(), signature), "SignatureBouncer: invalid signature for caller");
-        _;
-    }
-
-    /**
-     * @dev Requires that a valid signature with a specified method of a signer was provided.
-     */
-    modifier onlyValidSignatureAndMethod(bytes memory signature) {
-        // solhint-disable-next-line max-line-length
-        require(_isValidSignatureAndMethod(_msgSender(), signature), "SignatureBouncer: invalid signature for caller and method");
-        _;
-    }
-
-    /**
-     * @dev Requires that a valid signature with a specified method and params of a signer was provided.
-     */
-    modifier onlyValidSignatureAndData(bytes memory signature) {
-        // solhint-disable-next-line max-line-length
-        require(_isValidSignatureAndData(_msgSender(), signature), "SignatureBouncer: invalid signature for caller and data");
-        _;
-    }
-
-    /**
-     * @dev is the signature of `this + account` from a signer?
-     * @return bool
-     */
-    function _isValidSignature(address account, bytes memory signature) internal view returns (bool) {
-        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account)), signature);
-    }
-
-    /**
-     * @dev is the signature of `this + account + methodId` from a signer?
-     * @return bool
-     */
-    function _isValidSignatureAndMethod(address account, bytes memory signature) internal view returns (bool) {
-        bytes memory msgData = _msgData();
-        bytes memory data = new bytes(_METHOD_ID_SIZE);
-        for (uint256 i = 0; i < data.length; i++) {
-            data[i] = msgData[i];
-        }
-        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
-    }
-
-    /**
-     * @dev is the signature of `this + account + methodId + params(s)` from a signer?
-     * @notice the signature parameter of the method being validated must be the "last" parameter
-     * @return bool
-     */
-    function _isValidSignatureAndData(address account, bytes memory signature) internal view returns (bool) {
-        bytes memory msgData = _msgData();
-        require(msgData.length > _SIGNATURE_SIZE, "SignatureBouncer: data is too short");
-
-        bytes memory data = new bytes(msgData.length - _SIGNATURE_SIZE);
-        for (uint256 i = 0; i < data.length; i++) {
-            data[i] = msgData[i];
-        }
-
-        return _isValidDataHash(keccak256(abi.encodePacked(address(this), account, data)), signature);
-    }
-
-    /**
-     * @dev Internal function to convert a hash to an eth signed message
-     * and then recover the signature and check it against the signer role.
-     * @return bool
-     */
-    function _isValidDataHash(bytes32 hash, bytes memory signature) internal view returns (bool) {
-        address signer = hash.toEthSignedMessageHash().recover(signature);
-
-        return signer != address(0) && isSigner(signer);
-    }
-}