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/pgjwt.nix

@@ -13,7 +13,6 @@ stdenv.mkDerivation rec {
 
   buildPhase = ":";
   installPhase = ''
-    mkdir -p $out/bin  # current postgresql extension mechanism in nixos requires bin directory
     mkdir -p $out/share/extension
     cp pg*sql *.control $out/share/extension
   '';