nixos/treewide: Move rename.nix imports to their respective modules

A centralized list for these renames is not good because:
- It breaks disabledModules for modules that have a rename defined
- Adding/removing renames for a module means having to find them in the
central file
- Merge conflicts due to multiple people editing the central file

nixos/modules/system/boot/loader/loader.nix

@@ -3,6 +3,11 @@
 with lib;
 
 {
+  imports = [
+    (mkRenamedOptionModule [ "boot" "loader" "grub" "timeout" ] [ "boot" "loader" "timeout" ])
+    (mkRenamedOptionModule [ "boot" "loader" "gummiboot" "timeout" ] [ "boot" "loader" "timeout" ])
+  ];
+
     options = {
         boot.loader.timeout =  mkOption {
             default = 5;
@@ -12,4 +17,4 @@ with lib;
             '';
         };
     };
-}
+}