Replace obsolete QStyle::PM_DefaultChildMargin
While I just saw this by-passing accidentally, a quick note: all (edit: most of) these calls just set the values to the default values. You could also remove the calls, and the default values will still be used :)
I have seen similar things, and without having looked I suspect the current code is coming from having been ported away from KDialog:spacingHint/marginHint, and people had missed that layouts by themselves now default to the value from the style, so the porting should have just dropped explicit setting.
So you might want to inspect if you cannot make your code simpler by just dumping the explicit setting of values to what otherwise would fall back to the same default values.