nir: Delete nir_register::uses and nir_register::if_uses

We do piles of book-keeping work to keep track of them but never used
them for anything.

Acked-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
15 jobs for !588 with wip/nir-all-ssa in 13 minutes and 43 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
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ubuntu

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  Build+Test
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autotools

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meson-clang

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meson-gallium-clover-llvm

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meson-gallium-clover-llvm39

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meson-gallium-drivers-other

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meson-gallium-radeonsi

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meson-gallium-st-other

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meson-gallium-swr

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meson-glvnd

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meson-loader-classic-dri

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meson-vulkan

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scons-llvm

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scons-nollvm

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scons-swr

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