fix(webdav): remove spurious calendar_rest_handler module declaration

The declaration was brought in by a cherry-pick but that handler does
not exist on this branch, causing a compilation error.

src/interfaces/api/handlers/mod.rs

@@ -3,7 +3,6 @@ pub mod app_password_handler;
 pub mod auth_handler;
 pub mod batch_handler;
 pub mod caldav_handler;
-pub mod calendar_rest_handler;
 pub mod carddav_handler;
 pub mod chunked_upload_handler;
 pub mod contacts_handler;