postgresql: refactor to remove "this" argument

This was proposed by abbradar in #150801, but left out of the follow up PR
#221851 by Ma27 to reduce the size of the diff. Compared to the initial
proposal this includes the callPackage call in the recursion, which avoids
breaking the withJIT/withoutJIT helpers.

In terms of nixpkgs, this is a pure refactor, no derivations change. However,
this makes downstream expressions like the following possible:

  (postgresql.override { jitSupport = true; }).pkgs.postgis

This would have not worked before without passing another "this" argument,
which is error prone as can be seen in this example:

  https://github.com/PostgREST/postgrest/pull/3222/files

nixos/modules/services/databases/postgresql.md

@@ -277,7 +277,7 @@ self: super: {
 Here's a recipe on how to override a particular plugin through an overlay:
 ```
 self: super: {
-  postgresql_15 = super.postgresql_15.override { this = self.postgresql_15; } // {
+  postgresql_15 = super.postgresql_15// {
     pkgs = super.postgresql_15.pkgs // {
       pg_repack = super.postgresql_15.pkgs.pg_repack.overrideAttrs (_: {
         name = "pg_repack-v20181024";

pkgs/servers/sql/postgresql/default.nix

@@ -16,7 +16,6 @@ let
       self.lib.nameValuePair attrName (import path {
         inherit jitSupport self;
         thisAttr = attrName;
-        this = self.${attrName};
       })
     ) versions;
 

pkgs/servers/sql/postgresql/generic.nix

@@ -12,7 +12,7 @@ let
       , gssSupport ? with stdenv.hostPlatform; !isWindows && !isStatic
 
       # for postgresql.pkgs
-      , this, self, newScope, buildEnv
+      , self, newScope, buildEnv
 
       # source specification
       , version, hash, muslPatches
@@ -32,7 +32,7 @@ let
       # detection of crypt fails when using llvm stdenv, so we add it manually
       # for <13 (where it got removed: https://github.com/postgres/postgres/commit/c45643d618e35ec2fe91438df15abd4f3c0d85ca)
       , libxcrypt
-    }:
+    } @args:
   let
     atLeast = lib.versionAtLeast version;
     olderThan = lib.versionOlder version;
@@ -215,9 +215,9 @@ let
     disallowedReferences = [ stdenv'.cc ];
 
     passthru = let
+      this = self.callPackage generic args;
       jitToggle = this.override {
         jitSupport = !jitSupport;
-        this = jitToggle;
       };
     in
     {

pkgs/top-level/all-packages.nix

@@ -26748,8 +26748,8 @@ with pkgs;
     postgresql_15_jit
     postgresql_16_jit
   ;
-  postgresql = postgresql_15.override { this = postgresql; };
-  postgresql_jit = postgresql_15_jit.override { this = postgresql_jit; };
+  postgresql = postgresql_15;
+  postgresql_jit = postgresql_15_jit;
   postgresqlPackages = recurseIntoAttrs postgresql.pkgs;
   postgresqlJitPackages = recurseIntoAttrs postgresql_jit.pkgs;
   postgresql12Packages = recurseIntoAttrs postgresql_12.pkgs;