component/fontconfig: don't add default system fonts

By default, /usr/X11R6/lib/X11 /usr/X11/lib/X11 /usr/lib/X11 are added
if they exist at compile time
https://cgit.freedesktop.org/fontconfig/tree/configure.ac?id=b546940435ebfb0df575bc7a2350d1e913919c34#n502
We prefer isolation from base system

Remove the comment questioning about --add-default-font because we don't
add fonts for this reason and also because users can use a $FONTCONFIG
file.

component/fontconfig/buildout.cfg

@@ -18,12 +18,12 @@ shared = true
 url = http://fontconfig.org/release/fontconfig-2.12.6.tar.bz2
 md5sum = 733f5e2371ca77b69707bd7b30cc2163
 pkg_config_depends = ${freetype:pkg_config_depends}:${freetype:location}/lib/pkgconfig:${libxml2:location}/lib/pkgconfig
-# XXX-Cedric : should we use --with-add-fonts={somefont:location}/share,{someotherfont:location}/share?
 configure-options =
   --disable-static
   --disable-docs
   --enable-libxml2
   --with-default-fonts=${fonts:location}
+  --with-add-fonts=no
 environment =
   PATH=${pkgconfig:location}/bin:${gperf:location}/bin:%(PATH)s
   PKG_CONFIG_PATH=${:pkg_config_depends}