i965/fs: Do dead code elimination just after copy propagation.

i965/fs: Do dead code elimination just after copy propagation.

If we put the register coalescing in between the two, then we end up with code
sequences involving dead writes that the dead code elimination doesn't know
how to remove.  In place of making dead code elimination smart (which we
should do, too), make it less important for the moment.

shader-db results:

total instructions in shared programs: 722240 -> 721275 (-0.13%)
instructions in affected programs:     50573 -> 49608 (-1.91%)

(no shaders regressed).

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>