Fixes for -Wunused-function on Linux, Android and ChromeOS

chromeos/network/onc/onc_validator.cc

Index: chromeos/network/onc/onc_validator.cc
diff --git a/chromeos/network/onc/onc_validator.cc b/chromeos/network/onc/onc_validator.cc
index 29e58ac7b53797ab4bed815e2a7d536eb00bb151..d1d4c5203b443df0db3583f56922a365da9c7dc2 100644
--- a/chromeos/network/onc/onc_validator.cc
+++ b/chromeos/network/onc/onc_validator.cc
@@ -20,12 +20,6 @@ namespace onc {
 
 namespace {
 
-std::string ValueToString(const base::Value& value) {
-  std::string json;
-  base::JSONWriter::Write(&value, &json);
-  return json;
-}
-
 // Copied from policy/configuration_policy_handler.cc.
 // TODO(pneubeck): move to a common place like base/.
 std::string ValueTypeToString(base::Value::Type type) {