postgresql: refactor attributes

There is no need to call the `withoutJIT` passthru explicitly here - the
default is without JIT anyway. This allows us to change the passthru to
work differently *without* affecting every `postgresql_xx` top-level
package.

(cherry picked from commit a0b09dd7a1)

pkgs/servers/sql/postgresql/default.nix

@@ -23,7 +23,7 @@ let
       let
         attrName = if jitSupport then "${version}_jit" else version;
         postgresql = import path { inherit self; };
-        attrValue = if jitSupport then postgresql.withJIT else postgresql.withoutJIT;
+        attrValue = if jitSupport then postgresql.withJIT else postgresql;
       in
       self.lib.nameValuePair attrName attrValue
     ) versions;