Remove changeEvent(QEvent::LanguageChange) implementation

This was implemented only for a small set of widgets. It's unlikely that
we will ever have or even want a dynamic language selection, until then
this code is only dead freight.

Change-Id: I1bff4e1e89057786c0e5cb57225a508c5d390d9c
Reviewed-by: Eike Ziller <eike.ziller@digia.com>