[calamares] Drop #warning about KDSAG

- it might not be very current, and it's *probably* better to
  use dbus-activation / kf5dbus, but let's not call it
  deprecated until very sure that the dbus version does the
  right thing.

src/calamares/main.cpp

@@ -17,7 +17,6 @@
 #include "utils/Retranslator.h"
 
 #ifndef WITH_KF5DBus
-#warning "KDSingleApplicationGuard is deprecated"
 #include "3rdparty/kdsingleapplicationguard/kdsingleapplicationguard.h"
 #endif