fix nextcloud (case when enabled)

Previously, second mkIf for cleanup case took precedence when merge with
`//`. Now it's 2 modules: one for selfprivacy.modules.nextcloud.enable
== true, another for selfprivacy.modules.nextcloud.enable == false.

sp-modules/nextcloud/cleanup-module.nix

@@ -0,0 +1,19 @@
+{ config, lib, ... }:
+let
+  inherit (import ./common.nix config) sp db-pass-filepath admin-pass-filepath;
+in
+# FIXME do we really want to delete passwords on module deactivation!?
+{
+  config = lib.mkIf (!sp.modules.nextcloud.enable) {
+    system.activationScripts.nextcloudSecrets =
+      lib.trivial.warn
+        (
+          "nextcloud service is disabled, " +
+          "${db-pass-filepath} and ${admin-pass-filepath} will be removed!"
+        )
+        ''
+          rm -f ${db-pass-filepath}
+          rm -f ${admin-pass-filepath}
+        '';
+  };
+}