aco: don't propagate WQM for p_as_uniform

aco: don't propagate WQM for p_as_uniform

This was needed, so that in case of active helper lanes,
these contain the correct value. It is now handled implicitly.

Totals from 1004 (0.74% of 134913) affected shaders: (GFX10.3)
CodeSize: 7581020 -> 7580892 (-0.00%); split: -0.00%, +0.00%
Instrs: 1454940 -> 1454908 (-0.00%); split: -0.00%, +0.00%
Latency: 12984953 -> 12984894 (-0.00%); split: -0.00%, +0.00%
InvThroughput: 3173037 -> 3173049 (+0.00%); split: -0.00%, +0.00%
PreSGPRs: 47498 -> 47273 (-0.47%)

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14951>