meta: Merge timezone and locale with system

Usually one would want to define all of these options at the same time,
so it doesn't make sense to require importing several different modules.

For values that aren't needed, users can either override the configuration
in their own module or use an option that has been written upstream for the
module.

modules/locale.nix

@@ -1,4 +0,0 @@
-{
-  i18n.defaultLocale = "ja_JP.UTF-8";
-  i18n.supportedLocales = [ "ja_JP.UTF-8/UTF-8" "en_US.UTF-8/UTF-8" "fr_FR.UTF-8/UTF-8" ];
-}

modules/system.nix

@@ -1,3 +1,8 @@
 {
+  time.timeZone = "America/New_York";
+
+  i18n.defaultLocale = "ja_JP.UTF-8";
+  i18n.supportedLocales = [ "ja_JP.UTF-8/UTF-8" "en_US.UTF-8/UTF-8" "fr_FR.UTF-8/UTF-8" ];
+
   system.stateVersion = "22.11";
 }

modules/timezone.nix

@@ -1,3 +0,0 @@
-{
-  time.timeZone = "America/New_York";
-}