Revert "draw: revert using correct order for prim decomposition."

This reverts commit f97b731c82.

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/250

Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/gallium/auxiliary/draw/draw_pt_decompose.h

    const boolean quads_flatshade_last =      \
       draw->quads_always_flatshade_last;     \
    const boolean last_vertex_last =          \
-      !(draw->rasterizer->flatshade &&       \
-        draw->rasterizer->flatshade_first);
-/* FIXME: the draw->rasterizer->flatshade part is really wrong */
+      !draw->rasterizer->flatshade_first;
 
 #include "draw_decompose_tmp.h"