Clean up "performance allocators" and "performance flate2" backends #467

Job	Run time
macos-aarch64	4m 47s
sdist	4m 59s
linux (x86_64-unknown-linux-gnu)	4m 47s
macos-x86_64	4m 44s
linux (i686-unknown-linux-gnu)	4m 46s
linux-arm (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	4m 49s
linux-arm (armv7-unknown-linux-gnueabihf, armv7)	4m 45s
windows (x86_64-pc-windows-msvc, x64)	4m 40s
linux-powerpc (powerpc64le-unknown-linux-gnu, ppc64le)	4m 46s
windows (i686-pc-windows-msvc, x86)	4m 44s
linux-powerpc (powerpc64-unknown-linux-gnu, ppc64)	4m 45s
linux-arm (arm-unknown-linux-musleabihf, arm)	4m 46s
linux-s390x (s390x-unknown-linux-gnu, s390x)	4m 45s
musllinux (x86_64-unknown-linux-musl)	4m 50s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	4m 44s
musllinux (i686-unknown-linux-musl)	4m 45s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	4m 43s
musllinux-cross (powerpc64le-unknown-linux-musl, ppc64le, nightly)	4m 44s
	1h 25m 49s

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