aco: remove superflous (bool & exec) if the result comes from VOPC

aco: remove superflous (bool & exec) if the result comes from VOPC

This works in cases where the VOPC instruction was executed with
the same exec mask.

Totals from affected shaders: (VEGA)
SGPRS: 1342204 -> 1342164 (-0.00 %)
VGPRS: 877220 -> 877220 (0.00 %)
Spilled SGPRs: 157800 -> 157800 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 118083212 -> 118021748 (-0.05 %) bytes
LDS: 26 -> 26 (0.00 %) blocks
Max Waves: 144024 -> 144024 (0.00 %)

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5563>