ac/nir: Remove unhelpful nir_opt_cse from ac_nir_lower_ngg_nogs.

ac/nir: Remove unhelpful nir_opt_cse from ac_nir_lower_ngg_nogs.

This CSE call adds to our compile time without adding any real
benefit to the compiled code.

Fossil DB results on Sienna Cichlid (with NGGC on):

Totals from 1580 (1.23% of 128647) affected shaders:
CodeSize: 4563912 -> 4562312 (-0.04%); split: -0.07%, +0.03%
Instrs: 870722 -> 870338 (-0.04%); split: -0.09%, +0.04%
Latency: 3349863 -> 3351458 (+0.05%); split: -0.10%, +0.14%
InvThroughput: 617796 -> 617971 (+0.03%); split: -0.01%, +0.03%
VClause: 22604 -> 22568 (-0.16%); split: -0.75%, +0.59%
SClause: 16285 -> 16327 (+0.26%); split: -0.07%, +0.33%
Copies: 83472 -> 83599 (+0.15%); split: -0.07%, +0.22%
PreSGPRs: 62340 -> 62334 (-0.01%)

No Fossil DB changes with NGGC off.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11908>