i965: remove GLSL IR optimisation loop

i965: remove GLSL IR optimisation loop

IVB is running into some spilling issues in piglit with the
loop removed. However those tests are not really reflective
of a real world use case, also fp64 is brand new to IVB
so we leave the spilling issues to be resolved at a later
time.

Run time for shader-db on my machine goes from ~795 seconds to
~665 seconds.

shader-db results BDW:

total instructions in shared programs: 12969459 -> 12968891 (-0.00%)
instructions in affected programs: 1463154 -> 1462586 (-0.04%)
helped: 3622
HURT: 3326

total cycles in shared programs: 246453572 -> 246504318 (0.02%)
cycles in affected programs: 208842622 -> 208893368 (0.02%)
helped: 24029
HURT: 35407

total loops in shared programs: 2931 -> 2931 (0.00%)
loops in affected programs: 0 -> 0
helped: 0
HURT: 0

total spills in shared programs: 14560 -> 14498 (-0.43%)
spills in affected programs: 2270 -> 2208 (-2.73%)
helped: 17
HURT: 2

total fills in shared programs: 19671 -> 19632 (-0.20%)
fills in affected programs: 2060 -> 2021 (-1.89%)
helped: 17
HURT: 2

LOST:   17
GAINED: 40

Most of the hurt shaders are 1-2 instructions, with what looks like a max of 7.

I've looked at the worst cycles regressions and as far as I can tell its just
a scheduling difference.

Acked-by: Elie Tournier <elie.tournier@collabora.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>