Revert "pan/bi: Fix load_const of 1-bit booleans"

This reverts commit 29d319c7.

Now that we use nir_lower_bool_to_bitsize, we don't see 1-bit booleans
anymore, so the issue this fixed doesn't apply. Actually, that issue was
(in part) why I started looking into boolean handling in the first
place.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
103 jobs for !14576 with lower-bool-new in 17 minutes and 21 seconds (queued for 19 seconds)
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