Redundant distro branches

[Daniel van Vugt]

We've been using this as our distro branch for a while, but actually the 
distro does not use it:
    https://code.launchpad.net/~mir-team/mir/ubuntu

Why don't we just target future releases to the actual ubuntu (proposed) 
branch instead?
    https://code.launchpad.net/ubuntu/+source/mir

Presently I'm guessing most of ~mir-team can't write to those branches, 
but that's OK... we probably only need to be able to propose to them. No 
write access required.