mock out price accumulator

contracts/libraries/MOCK_Decimal.sol

@@ -0,0 +1,20 @@
+pragma solidity 0.5.12;
+
+// mock fixed- or floating-point math
+library MOCK_Decimal {
+    struct Decimal {
+        uint256 data;
+    }
+
+    function div(uint128 numerator, uint128 denominator) internal pure returns (Decimal memory) {
+        return Decimal(numerator / denominator);
+    }
+
+    function mul(Decimal memory a, uint128 b) internal pure returns (Decimal memory) {
+        return Decimal(a.data * b);
+    }
+
+    function add(Decimal memory a, Decimal memory b) internal pure returns (Decimal memory) {
+        return Decimal(a.data + b.data);
+    }
+}

contracts/libraries/SafeMath128.sol

@@ -10,15 +10,4 @@ library SafeMath128 {
     function mul(uint128 x, uint128 y) internal pure returns (uint128 z) {
         require(y == 0 || (z = x * y) / y == x, "ds-math-mul-overflow");
     }
-
-    function oadd(uint128 w, uint128 x) internal pure returns (uint128 y, uint128 z) {
-        uint256 sum = uint256(w) + x;
-        z = uint128(sum / uint128(-1));
-        y = uint128(sum % uint128(-1));
-    }
-    function omul(uint128 w, uint128 x) internal pure returns (uint128 y, uint128 z) {
-        uint256 product = uint256(w) * x;
-        z = uint128(product / uint128(-1));
-        y = uint128(product % uint128(-1));
-    }
 }