Remove obsolete forced setting of XDG_CONFIG_HOME.

Apparently this was introduced in 2011 as a workaround to solve a problem in
libimobiledevice. However already in 2013 the problem was solved
in libimobiledevice:
b811fbb05b

src/main.cpp

@@ -302,14 +302,6 @@ int main(int argc, char* argv[]) {
     }
   }
 
-#ifdef Q_OS_DARWIN
-  // Must happen after QCoreApplication::setOrganizationName().
-  setenv(
-      "XDG_CONFIG_HOME",
-      Utilities::GetConfigPath(Utilities::Path_Root).toLocal8Bit().constData(),
-      1);
-#endif
-
   // Output the version, so when people attach log output to bug reports they
   // don't have to tell us which version they're using.
   qLog(Info) << "Clementine-qt5" << CLEMENTINE_VERSION_DISPLAY;