Revert "pstree: remove and alias to psmisc"

This reverts commit 4f8bf685f8.

Reason: psmisc is Linux-platforms only

pkgs/applications/misc/pstree/default.nix

@@ -0,0 +1,25 @@
+{ stdenv, fetchurl }:
+
+stdenv.mkDerivation rec {
+  name = "pstree-2.39";
+
+  src = fetchurl {
+    urls = [
+      "http://www.sfr-fresh.com/unix/misc/${name}.tar.gz"
+      "https://distfiles.macports.org/pstree/${name}.tar.gz"
+    ];
+    sha256 = "17s7v15c4gryjpi11y1xq75022nkg4ggzvjlq2dkmyg67ssc76vw";
+  };
+
+  unpackPhase = "unpackFile \$src; sourceRoot=.";
+
+  buildPhase = "pwd; $CC -o pstree pstree.c";
+  installPhase = "mkdir -p \$out/bin; cp pstree \$out/bin";
+
+  meta = {
+    description = "Show the set of running processes as a tree";
+    license = "GPL";
+    maintainers = [ ];
+    platforms = stdenv.lib.platforms.unix;
+  };
+}

pkgs/top-level/aliases.nix

@@ -256,7 +256,6 @@ mapAliases ({
   # end
   ppl-address-book = throw "deprecated in 2019-05-02: abandoned by upstream.";
   procps-ng = procps; # added 2018-06-08
-  pstree = psmisc; # added 2019-05-05
   pulseaudioLight = pulseaudio; # added 2018-04-25
   qca-qt5 = libsForQt5.qca-qt5;  # added 2015-12-19
   qt_gstreamer = qt-gstreamer;  # added 2017-02

pkgs/top-level/all-packages.nix

@@ -19572,6 +19572,8 @@ in
 
   psol = callPackage ../development/libraries/psol { };
 
+  pstree = callPackage ../applications/misc/pstree { };
+
   ptask = callPackage ../applications/misc/ptask { };
 
   pulseaudio-ctl = callPackage ../applications/audio/pulseaudio-ctl { };