fontconfig-ultimate: fixup after bash update

I've got no idea why it was trying to override the phase list and in
such a way. Still, it's slightly discomforting that the expansion
semantics was changed in bash.

pkgs/development/libraries/fontconfig-ultimate/default.nix

···
     owner = "bohoomil";
   };
 
-  phases = "$prePhases unpackPhase installPhase $postPhases";
-
   installPhase = ''
     mkdir -p $out/etc/fonts/conf.d
     cp conf.d.infinality/*.conf $out/etc/fonts/conf.d