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

1 files changed, 0 insertions, 1 deletions

diff --git a/pkgs/servers/sql/postgresql/default.nix b/pkgs/servers/sql/postgresql/default.nix
index d8acae8787a63..d11a2d06b2d26 100644
--- a/pkgs/servers/sql/postgresql/default.nix
+++ b/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;