postgresql: always create the $out/bin directory

This is needed because some PostgreSQL plugins don't have a bin
directory. If only these plugins are listed in cfg.extraPlugins buildEnv
will turn $out/bin into a symbolic link to ${pg}/bin. Lateron we try to
rm $out/bin/{pg_config,postgres,pg_ctl} which will then fail because
$out/bin will be read-only.

pkgs/servers/sql/postgresql/ext/timescaledb.nix

@@ -34,13 +34,6 @@ stdenv.mkDerivation rec {
     done
   '';
 
-  postInstall = ''
-    # work around an annoying bug, by creating $out/bin, so buildEnv doesn't freak out later
-    # see https://github.com/NixOS/nixpkgs/issues/22653
-
-    mkdir -p $out/bin
-  '';
-
   meta = with stdenv.lib; {
     description = "Scales PostgreSQL for time-series data via automatic partitioning across time and space";
     homepage    = https://www.timescale.com/;