Bug 1597739 - Remove MinGW define for ASSOCF_NONE r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D55996

--HG--
extra : moz-landing-system : lando

uriloader/exthandler/win/nsOSHelperAppService.cpp

@@ -27,10 +27,6 @@
 
 #define LOG(args) MOZ_LOG(mLog, mozilla::LogLevel::Debug, args)
 
-#ifdef __MINGW32__
-#  define ASSOCF_NONE 0x0
-#endif
-
 // helper methods: forward declarations...
 static nsresult GetExtensionFromWindowsMimeDatabase(const nsACString& aMimeType,
                                                     nsString& aFileExtension);