r300: remove the nrt main optimization loop

r300: remove the nrt main optimization loop

Most of it is already called during finalize_nir, so here we do just some final
polishing.

This brings some minor but reproducible compile-time speedups (dEQP on my RV370
and AMD Ryzen 9 3900X at 8 threads goes from 80s to 74s).

RV530 shader-db:
total instructions in shared programs: 130303 -> 130275 (-0.02%)
instructions in affected programs: 1661 -> 1633 (-1.69%)
helped: 9
HURT: 2

instructions helped:   shaders/godot3.4/10-36.shader_test FS:            163 -> 162 (-0.61%)
instructions helped:   shaders/tropics/240.shader_test VS:               144 -> 140 (-2.78%)
instructions helped:   shaders/tropics/246.shader_test VS:               137 -> 133 (-2.92%)
instructions helped:   shaders/tropics/222.shader_test VS:               131 -> 127 (-3.05%)
instructions helped:   shaders/tropics/228.shader_test VS:               128 -> 124 (-3.12%)
instructions helped:   shaders/tropics/252.shader_test VS:               126 -> 122 (-3.17%)
instructions helped:   shaders/tropics/234.shader_test VS:               121 -> 117 (-3.31%)
instructions helped:   shaders/tropics/216.shader_test VS:               104 -> 100 (-3.85%)
instructions helped:   shaders/tropics/210.shader_test VS:               101 -> 97 (-3.96%)

instructions HURT:   shaders/yofrankie/15.shader_test FS:              211 -> 213 (0.95%)
instructions HURT:   shaders/yofrankie/42.shader_test FS:              295 -> 298 (1.02%)

Signed-off-by: Pavel Ondračka <pavel.ondracka@gmail.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Filip Gawin <filip.gawin@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23437>