Bug#655210: installation-guide: please remove the "preseed-X" part from translations too

[Timo Aaltonen <timo.aaltonen@canonical.com>]

Source: installation-guide
Severity: normal

I noticed that the translations still have the "preseed-X" part of 
preseed documentation on them, which got removed from 
en/appendix/preseed.xml over three years ago. It should be removed from 
the po/*/preseed.po files too.