[Merge] ~nteodosio/update-manager:installnow into update-manager:main

[Nathan Teodosio]

Another possibility would be to just make the button insensitive, which is what actually happens when Pro is not involved, but removing the button was in the design.
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https://code.launchpad.net/~nteodosio/update-manager/+git/update-manager/+merge/474637
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