Remove calls to setAttribute for "AA_UseHighDpiPixmaps" now useless
For instance
/home/meven/kde6/src/plasma-desktop/emojier/app/emojier.cpp: In function ‘int main(int, char**)’:
/home/meven/kde6/src/plasma-desktop/emojier/app/emojier.cpp:77:26: warning: ‘Qt::AA_UseHighDpiPixmaps’ is deprecated: High-DPI pixmaps are always enabled. This attribute no longer has any effect. [-Wdeprecated-declarations]