NaCl SDK: Remove some unused variables in url_loader.cc example

native_client_sdk/src/examples/api/url_loader/url_loader.cc

Index: native_client_sdk/src/examples/api/url_loader/url_loader.cc
diff --git a/native_client_sdk/src/examples/api/url_loader/url_loader.cc b/native_client_sdk/src/examples/api/url_loader/url_loader.cc
index d000a93cd14e9f83aaa34f115974759712665c29..7af8c6e50fb76f7a121786ffb90afc67ae5dfebf 100644
--- a/native_client_sdk/src/examples/api/url_loader/url_loader.cc
+++ b/native_client_sdk/src/examples/api/url_loader/url_loader.cc
@@ -17,11 +17,6 @@
 namespace {
 const char* const kLoadUrlMethodId = "getUrl";
 static const char kMessageArgumentSeparator = ':';
-
-// Exception strings.  These are passed back to the browser when errors
-// happen during property accesses or method calls.
-const char* const kExceptionStartFailed = "URLLoaderHandler::Start() failed";
-const char* const kExceptionURLNotAString = "URL is not a string";
 }  // namespace
 
 class URLLoaderInstance : public pp::Instance {