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/pgrouting.nix

@@ -15,7 +15,6 @@ stdenv.mkDerivation rec {
   };
 
   installPhase = ''
-    mkdir -p $out/bin # for buildEnv, see https://github.com/NixOS/nixpkgs/issues/22653
     install -D lib/*.so                        -t $out/lib
     install -D sql/pgrouting--${version}.sql   -t $out/share/extension
     install -D sql/common/pgrouting.control    -t $out/share/extension