Please retire extras.ubuntu.com

[Dimitri John Ledkov]

At the moment do-release-upgrade -d from utopic -> vivid is failing
because extras.ubuntu.com repository does not exist for vivid, it's
failing to fetch and thus upgrade is aborted becase of "possible
network problems".

Can we please stop adding extras.ubuntu.com by default? Not consider
it's absence as failure to upgrade Ubuntu? Have it in apt.sources.d/*
instead of apt.sources?

Quantal appears to be the last release that had extras.ubuntu.com.

Unless there are any objects I'll remove extras.ubuntu.com from new
installations and will seek SRU to trusty and up to drop
extras.ubuntu.com from the apt.sources.

-- 
Regards,

Dimitri.