Remove built-in valgrind support due to GNUisms #399

Job	Run time
build-linux-glibc	50s
build-linux-glibc-arm	2m 10s
build-linux-glibc-arm64	1m 35s
build-linux-musl-arm	1m 34s
build-linux-musl	1m 52s
build-linux-musl-arm64	2m 7s
build-macos-arm64	55s
build-macos-x64	54s
build-windows	2m 45s
pack	0s
build-test-binaries	0s
run-test-binaries-cross-plat	0s
run-test-binaries-os-versions	0s
	14m 42s

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