[packagekit] Getting rid of stderr

[Richard Hughes]

With the legacy non-dbus backends we currently output commands on stderr
and stdout. I think it would be a lot easier if we output all the
commands on stdout, and then we can:

* get rid of a ton of code
* make testing easier
* get rid of the flushing problem we have now, where we cannot guarantee
that we can get the events in the correct order.

It's a pretty trivial bit of code.

Sane?

Richard.