xfont_font-util: enable host package

When compiling xfonts, host utilities like bdftopcf or ucs2any, part
of xfont_font-util are needed. Until now, xfont_font-util was
installing ugly symbolic links, assuming that these tools were
available on the development machine.

This patch enables the host package for xfont_font-util, removes the
post-install.sh script, and keeps only the useful part of this script
in a post install hook.

host-xfont_font-util will be used later by xfont packages.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>