postgresql: cleanup postgis

[danbst]

Motivation for this change

• remove unneeded code
• make sure GDAL doesn't use wrong PG version
• pin poppler to an older version, to prevent future GDAL<->poppler API breaks (on poppler updates)
• split 35Mb of docs into separate output

This is rebased and depends on #54319

cc @ingenieroariel @thoughtpolice

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[ingenieroariel]

I tested it and it works just as master does (but using postgresql 11). The incantation is a bit ugly (mostly based on stolen code):

let
  pkgs = import (fetchTarball "https://github.com/danbst/nixpkgs/archive/afb270f60a8b9721741538d8fb563a73302cd39d.tar.gz") {};
  stdenv = pkgs.stdenv;
  pg = (pg:
      pkgs.buildEnv {
        name = "postgresql-and-plugins-${(builtins.parseDrvName pg.name).version}";
        paths = [ pg pg.lib (pkgs.postgresqlPackages.postgis.override { postgresql = pg; }) ];
        buildInputs = [ pkgs.makeWrapper ];
        postBuild = ''
          mkdir -p $out/bin
          rm $out/bin/{pg_config,postgres,pg_ctl}
          cp --target-directory=$out/bin ${pg}/bin/{postgres,pg_config,pg_ctl}
          wrapProgram $out/bin/postgres --set NIX_PGLIBDIR $out/lib
        '';
      }
    );
in stdenv.mkDerivation rec {
    name = "postgistest";
    buildInputs = with pkgs; [ (pg postgresql_11) ];
    shellHook =
  ''
    export PGDATA=`pwd`/data
    initdb --no-locale --encoding=UTF-8
    pg_ctl -D $PGDATA -l "$PGDATA/server.log" start
    sleep 2
    createdb postgistest
    psql postgistest -c "CREATE EXTENSION postgis;"
    psql postgistest -c "CREATE EXTENSION postgis_topology;"
    psql postgistest -c "SELECT ST_GeomFromText('POINT(1 1)');"
  '';
}

[danbst]

@ingenieroariel much thanks for your test! BTW, with this PR you can simplify expression down to:

    let
      pkgs = import (fetchTarball "https://github.com/danbst/nixpkgs/archive/afb270f60a8b9721741538d8fb563a73302cd39d.tar.gz") {};
      pg = pkgs.postgresql_11.withPackages (ps: [   # ps stands for "plugins" or "packages"
          ps.postgis
      ]);
    in pkgs.mkShell rec {
        name = "postgistest";
        buildInputs = [ pg ];
        shellHook = ''
            export PGDATA=$PWD/data
            pg_ctl -D $PGDATA initdb -w
            pg_ctl -D $PGDATA -l "$PGDATA/server.log" start -w
            createdb postgistest
            psql postgistest -c "CREATE EXTENSION postgis;"
            psql postgistest -c "CREATE EXTENSION postgis_topology;"
            psql postgistest -c "SELECT ST_GeomFromText('POINT(1 1)');"
        '';
    };

[nixos-discourse]

This pull request has been mentioned on Nix community. There might be relevant details there:

https://discourse.nixos.org/t/heads-up-upcoming-changes-to-the-postgresql-infrastructure-and-nixos-module/297/5