Revert commit 902991 (and a related BC-maintaining commit which is now unnecessary).
This commit was intended to improve support for accented characters from what I gather but it moved the keyPress event handler to act on key release instead which is causing bug 179205 (KLineEdits have actions using Ctrl key duplicated twice).
This is because pasting on key release doesn't stop Qt from pasting on key press (and we can't just disable various Qt actions on key press as that's really an implementation detail for Qt IMO).

I'm sure there is a way to implement the accented chars thing that makes everyone happy but I'd rather fix the more pressing bug at this point.