nir/algebraic: remove duplicate bool conversion lowerings

nir/algebraic: remove duplicate bool conversion lowerings

While [1] added some boolean conversion lowering patterns, those were
already dealt with on [2].

[1] - b86305bb ("nir/algebraic: collapse conversion opcodes (many patterns)")
[2] - d7e0d47b ("nir/algebraic: nir: Add a bunch of b2[if] optimizations")

Fixes: b86305bb ("nir/algebraic: collapse conversion opcodes (many patterns)")
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Signed-off-by: Isabella Basso <isabellabdoamaral@usp.br>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20965>