Remove unused errorMessage

Change-Id: If799737a69545bf6789213ce3f4dd6c724352213
diff --git a/tools/bit/make.cpp b/tools/bit/make.cpp
index c39f494..2a88732 100644
--- a/tools/bit/make.cpp
+++ b/tools/bit/make.cpp
@@ -90,8 +90,7 @@
 
     Json::Value json;
     Json::CharReaderBuilder builder;
-    std::string errorMessage;
-    if (!Json::parseFromStream(builder, stream, &json, &errorMessage)) {
+    if (!Json::parseFromStream(builder, stream, &json, /* errorMessage = */ nullptr)) {
         return;
     }
 
@@ -215,8 +214,7 @@
 
     Json::Value json;
     Json::CharReaderBuilder builder;
-    std::string errorMessage;
-    if (!Json::parseFromStream(builder, stream, &json, &errorMessage)) {
+    if (!Json::parseFromStream(builder, stream, &json, /* errorMessage = */ nullptr)) {
         json_error(filename, "can't parse json format", quiet);
         return;
     }