dosemu-fonts: Fix and simplify build

Regression introduced by 9820cb1b

.

The commit only sets dontBuild but the build for the DOSEmu fonts had a
dummy configurePhase as well.

So rather than just reinserting a dummy configurePhase again, let's just
use buildCommand and put it out in one go, which is more suitable for
such a simple package.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>