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/services/monitoring/prometheus/alertmanager.nix

@@ -27,6 +27,15 @@ let
       "--log.format ${cfg.logFormat}"
   );
 in {
+  imports = [
+    (mkRemovedOptionModule [ "services" "prometheus" "alertmanager" "user" ] "The alertmanager service is now using systemd's DynamicUser mechanism which obviates a user setting.")
+    (mkRemovedOptionModule [ "services" "prometheus" "alertmanager" "group" ] "The alertmanager service is now using systemd's DynamicUser mechanism which obviates a group setting.")
+    (mkRemovedOptionModule [ "services" "prometheus" "alertmanagerURL" ] ''
+      Due to incompatibility, the alertmanagerURL option has been removed,
+      please use 'services.prometheus2.alertmanagers' instead.
+    '')
+  ];
+
   options = {
     services.prometheus.alertmanager = {
       enable = mkEnableOption "Prometheus Alertmanager";