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/component.rs

@@ -82,6 +82,7 @@ pub fn init_component_items<Base>(
     })
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 pub(crate) mod ffi {
     #![allow(unsafe_code)]