[clipboard] kill onbefore* events?

Hi,
there's some scepticism about implementing
onbeforecut/onbeforepaste/onbeforecopy in Gecko [1], IE's implementation
seems considerably more limited than I expected (maybe because of bugs?),
and it doesn't really seem like an elegant solution to the use case it is
meant to solve.

Would anybody mind if we killed those events?

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=596764

-Hallvord R