Removed default value assignments. (#1432)

(cherry picked from commit cfef5836)

contracts/drafts/ERC1046/TokenMetadata.sol

@@ -13,7 +13,7 @@ contract ERC20TokenMetadata is IERC20 {
 }
 
 contract ERC20WithMetadata is ERC20TokenMetadata {
-  string private _tokenURI = "";
+  string private _tokenURI;
 
   constructor(string tokenURI)
     public

contracts/payment/SplitPayment.sol

@@ -24,8 +24,6 @@ contract SplitPayment {
     require(payees.length == shares.length);
     require(payees.length > 0);
 
-    _totalShares = 0;
-    _totalReleased = 0;
     for (uint256 i = 0; i < payees.length; i++) {
       _addPayee(payees[i], shares[i]);
     }

contracts/utils/ReentrancyGuard.sol

@@ -12,6 +12,8 @@ contract ReentrancyGuard {
   uint256 private _guardCounter;
 
   constructor() public {
+    // The counter starts at one to prevent changing it from zero to a non-zero
+    // value, which is a more expensive operation.
     _guardCounter = 1;
   }