Merge pull request #2469 from iced-rs/unify-shell-runtimes

`Daemon` API and Shell Runtime Unification

core/src/window/id.rs

@@ -11,9 +11,6 @@ pub struct Id(u64);
 static COUNT: AtomicU64 = AtomicU64::new(1);
 
 impl Id {
-    /// The reserved window [`Id`] for the first window in an Iced application.
-    pub const MAIN: Self = Id(0);
-
     /// Creates a new unique window [`Id`].
     pub fn unique() -> Id {
         Id(COUNT.fetch_add(1, atomic::Ordering::Relaxed))