nixos/fontconfig-penultimate: disable by default

It currently lacks an emoji font-family which means it has to be
disabled for them to function [0].  Additionally it's fallen out of
necessity to ship custom font rendering settings (as far as I'm aware
of).

[0]: NixOS#67215

nixos/doc/manual/release-notes/rl-1909.xml

@@ -585,6 +585,12 @@
       features.
     </para>
    </listitem>
+   <listitem>
+    <para>
+     We no longer enable custom font rendering settings with <option>fonts.fontconfig.penultimate.enable</option> by default.
+     The defaults from fontconfig are sufficient.
+    </para>
+   </listitem>
   </itemizedlist>
  </section>
 </section>

nixos/modules/config/fonts/fontconfig-penultimate.nix

@@ -269,7 +269,7 @@ in
         penultimate = {
           enable = mkOption {
             type = types.bool;
-            default = true;
+            default = false;
             description = ''
               Enable fontconfig-penultimate settings to supplement the
               NixOS defaults by providing per-font rendering defaults and