[Tails-dev] [review'n'merge] core files

ey there:

please review and merge this super tiny commit:

[afef14bd10] remove install/os from core_files

Available at git.tails.boum.org:emmapeel/tails

 * [new branch]            corefiles_update 

I take out the deleted page install/os from the core_files.txt, as it makes

`wiki/src/contribute/l10n_tricks/language_statistics.sh` fail.