Fix unused type in WASI #4335

Job	Run time
Check --no-default-features (nightly)	17s
Check selected Tier 3 platforms (nightly)	3m 20s
Check (stable)	1m 35s
Rustfmt	4s
Check (nightly)	1m 17s
Check (1.63)	1m 30s
Check nightly-only targets (nightly)	24s
Test rustix_use_experimental_asm (powerpc64le-linux)	46s
Test use-libc (ubuntu)	36s
Test (ubuntu)	44s
Test use-libc (i686-linux)	45s
Test (ubuntu-20.04)	46s
Test use-libc (aarch64-linux)	1m 2s
Test (i686-linux)	57s
Test use-libc (powerpc64le-linux)	1m 1s
Test (aarch64-linux)	1m 4s
Test use-libc (riscv64-linux)	55s
Test (powerpc64le-linux)	1m 13s
Test use-libc (arm-linux)	57s
Test (riscv64-linux)	1m 1s
Test (s390x-linux)	1m 9s
Test (arm-linux)	1m 2s
Test (ubuntu-stable)	42s
Test (i686-linux-stable)	54s
Test (aarch64-linux-stable)	1m 0s
Test (riscv64-linux-stable)	1m 11s
Test (s390x-linux-stable)	1m 16s
Test (powerpc64le-linux-stable)	58s
Test (arm-linux-stable)	1m 32s
Test (ubuntu-1.63)	1m 40s
Test (i686-linux-1.63)	1m 50s
Test (aarch64-linux-1.63)	1m 54s
Test (riscv64-linux-1.63)	2m 1s
Test (s390x-linux-1.63)	2m 4s
Test (powerpc64le-linux-1.63)	2m 20s
Test (arm-linux-1.63)	1m 54s
Test (macos-latest)	18m 12s
Test (macos-12)	18m 52s
Test (windows)	55s
Test (windows-2019)	54s
Test (musl)	41s
	1h 23m 15s

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