Remove extern "C" functions from wasm module

We don't need these functions and their export. They account for ~20kb in
the optimized .wasm - plus JS glue code.

sixtyfps_runtime/corelib/window.rs

@@ -271,6 +271,7 @@ impl ComponentWindow {
     }
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 /// This module contains the functions needed to interface with the event loop and window traits
 /// from outside the Rust language.
 pub mod ffi {