removed() is deprecated since 5.0 because the code has to downcast a partially
destroyed QObject back to a QAction (from the slot connected to
destroyed()). This is very dangerous, calling QAction methods will just
crash.
plasma-framework/src/scriptengines/qml/plasmoid/containmentinterface.cpp
is using that removed() signal, but doesn't care about the argument,
it's connecting both inserted() and removed() to a generic changed
signal used to notify QML.
For this use case, all we need in KActionCollection is a changed() signal
with no argument, emitted for both insertion and removal.
This makes me wonder if inserted() still is useful at all, but well, it
doesn't hurt to keep it.