Remove unused macro definition. (no bug) r=trivial

--HG--
extra : rebase_source : aeba3599fc93587dac5b0bdec0a693930819d446
extra : histedit_source : 67e620f78a22c62a6da39849bf7fcdf96ddac5e5

toolkit/mozapps/extensions/AddonManagerStartup.cpp

@@ -50,12 +50,6 @@ namespace mozilla {
 using Compression::LZ4;
 using dom::ipc::StructuredCloneData;
 
-#ifdef XP_WIN
-#  define READ_BINARYMODE "rb"
-#else
-#  define READ_BINARYMODE "r"
-#endif
-
 AddonManagerStartup& AddonManagerStartup::GetSingleton() {
   static RefPtr<AddonManagerStartup> singleton;
   if (!singleton) {