Update: Remove unused code for checking nightly build on AppVeyor

We have nightly builds on Github already.

Src/Lib/DownloadHelper.h

@@ -60,7 +60,6 @@ struct VersionData
 	};
 
 	TLoadResult Load(bool official);
-	TLoadResult LoadNightly();
 	TLoadResult Load( const wchar_t *fname, bool bLoadFlags );
 private:
 	void operator=( const VersionData& );