iris: Drop unused locals from iris_clear.c to avoid warning

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
10 jobs for !984 with r/iris-warnings in 8 minutes and 43 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Containers Build
passed debian #330451

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  Build+Test
passed meson-clang #330453

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passed meson-clover #330457

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passed meson-main #330456

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passed meson-swr-glvnd #330452

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passed meson-vulkan #330458

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passed scons-llvm #330460

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passed scons-nollvm #330459

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passed scons-swr #330454

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passed scons-win64 #330455

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