[Merge] lp:~xnox/ubuntu-release-upgrader/lp1409555 into lp:ubuntu-release-upgrader

[Brian Murray]

In the process of tracking down the test failure I also found a method for removing entries from sources.list, sources.list.remove(), and that seems like a better idea to me than creating a new list.
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https://code.launchpad.net/~xnox/ubuntu-release-upgrader/lp1409555/+merge/246233
Your team Ubuntu Core Development Team is requested to review the proposed merge of lp:~xnox/ubuntu-release-upgrader/lp1409555 into lp:ubuntu-release-upgrader.