Clean up "performance allocators" and "performance flate2" backends #482

Job	Run time
macos-aarch64	6m 52s
macos-x86_64	9m 42s
sdist	7m 0s
linux (x86_64-unknown-linux-gnu)	8m 7s
linux-arm (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	9m 9s
linux (i686-unknown-linux-gnu)	12m 10s
windows (x86_64-pc-windows-msvc, x64)	15m 54s
linux-arm (armv7-unknown-linux-gnueabihf, armv7)	8m 49s
windows (i686-pc-windows-msvc, x86)	15m 7s
linux-arm (arm-unknown-linux-musleabihf, arm)	8m 26s
linux-powerpc (powerpc64le-unknown-linux-gnu, ppc64le)	9m 9s
musllinux (x86_64-unknown-linux-musl)	8m 30s
linux-powerpc (powerpc64-unknown-linux-gnu, ppc64)	8m 39s
linux-s390x (s390x-unknown-linux-gnu, s390x)	12m 48s
musllinux (i686-unknown-linux-musl)	7m 55s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	9m 27s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	8m 9s
musllinux-cross (powerpc64le-unknown-linux-musl, ppc64le, nightly)	6m 58s
	2h 52m 51s

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