Some more livecd package set adjustments

[Matthias Clasen]

I'd like to drop krb5-auth-dialog from the live cd. 
Some reasons:
- It doesn't seem to be very relevant on the live cd
- It recently started adding another entry to our already overlong
preferences menu

We should also not forget to drop gst-mixer again, but that can probably
wait until Bastien lands his sound capplet enhancements.

Comments ?


Matthias