imagescaler: replace virtual font package with real package

fonts-sil-yi is a purely virtual package hence it is never going to
be installed. Instead it would install 'fonts-sil-nuosusil'.

Previous change 1818053d / https://gerrit.wikimedia.org/r/#/c/88441/ did
update the packages to no more point to virtual packages. Something must
have changed since or might have been a mistake.

On each run of puppet, it would find out that the 'fonts-sil-yi' is not
installed and reinstall it. That cause an even to be propagated which
eventually propage up to Service['apache'] which end up being restarted.

I dont think restarting Apache over and over is a good idea and we get
ton of "Caught SIGTERM, restarting" errors in Apache logs.

RT #6500

Change-Id: I6d6250e692217f3fe6ce0d9ba89ec35ba2088233