No longer override the default kernel font if nothing is specified in
vconsole.conf.

The default kernel font[0] provides ISO-8859-1 and box characters. Users
of Arabic, Cyrilic or Hebrew must set a different font manually as these
character sets were provided by the old default font [1], but are not
any longer.

Rationale:

 * it is counter-intuitive that an empty vconsole.conf file is different
   from adding FONT="";
 * the version of the default font shipped with Arch (which is the
   upstream one) behaves very badly during early boot[2] (which should
   admittedly be fixed in the font itself);
 * the kernel already supplies a default font, it seems reasonable to
   use that unless anything else is specified;
 * This also avoids a needless slow call to setfont; and
 * We don't want to work around problems in the kernel (in case the
   compiled-in font is not acceptable for whatever reason).

[0]: <https://dev.archlinux.org/~tomegun/kernel.bdf>
[1]: <https://dev.archlinux.org/~tomegun/latarcyrheb.bdf>
[2]: <http://i.imgur.com/J2tM4.jpg>