api: remove ::dummy from Id types

`::dummy` was used for testing purposes and became redundant after
adding e.g. `from_raw` and `into_raw` methods on `Id` types.

src/platform_impl/linux/wayland/event_loop/mod.rs

@@ -30,7 +30,7 @@ use sink::EventSink;
 
 use super::state::{WindowCompositorUpdate, WinitState};
 use super::window::state::FrameCallbackState;
-use super::{logical_to_physical_rounded, DeviceId, WindowId};
+use super::{logical_to_physical_rounded, WindowId};
 
 type WaylandDispatcher = calloop::Dispatcher<'static, WaylandSource<WinitState>, WinitState>;