Remove confusing debug message

This debug message is not helpful without knowing where it comes from.
In addition to that, it indicates that the lack of libinput connection is
bad, but it is not. For example, with the nested wayland compositor you
will never have a valid libinput connection, which is fine.

tabletmodemanager.cpp

@@ -75,7 +75,6 @@ public:
 
     void check() {
         if (!LibInput::Connection::self()) {
-            qDebug() << "no libinput :(";
             return;
         }
         const auto devices = LibInput::Connection::self()->devices();