Revert "mdadm: update from 3.3 to 3.3.2"

This reverts commit 1faf6106c3fc5890297ad6c8e26b572d91dede5a. It
causes the size of the initrd to explode from ~6 MB to 19 MB:

http://hydra.nixos.org/build/15728196

The reason is that mdadm now contains a self-reference:

$ strings ./result/sbin/mdadm | grep /nix/store
...
ACTION=="add", SUBSYSTEM=="block", ENV{DEVTYPE}=="%s", ENV{ID_PATH}=="%s", RUN+="/nix/store/y1ap6va0av6jhxf7ddnr8vdwxd7b44gd-mdadm-3.3.2/sbin/mdadm --incremental $env{DEVNAME}"
ACTION=="add", SUBSYSTEM=="block", ENV{ID_PATH}=="%s", RUN+="/nix/store/y1ap6va0av6jhxf7ddnr8vdwxd7b44gd-mdadm-3.3.2/sbin/mdadm --incremental $env{DEVNAME}"
/nix/store/y1ap6va0av6jhxf7ddnr8vdwxd7b44gd-mdadm-3.3.2/sbin/mdmon

(Previously, it referred to /sbin/mdadm.) This causes mdadm, glibc and
linux-headers to be added to the initrd.

pkgs/os-specific/linux/mdadm/default.nix

···
 { stdenv, fetchurl, groff }:
 
 stdenv.mkDerivation rec {
-  name = "mdadm-3.3.2";
+  name = "mdadm-3.3";
 
   src = fetchurl {
-    url = "mirror://kernel/linux/utils/raid/mdadm/${name}.tar.xz";
-    sha256 = "132vdvh3myjgcjn6i9w90ck16ddjxjcszklzkyvr4f5ifqd7wfhg";
+    url = "mirror://kernel/linux/utils/raid/mdadm/${name}.tar.bz2";
+    sha256 = "0igdqflihiq1dp5qlypzw0xfl44f4n3bckl7r2x2wfgkplcfa1ww";
   };
 
   nativeBuildInputs = [ groff ];