Remove __wbindgen_thread_id

After talking to John, he mentioned that this function was once
implemented in Wasmer, but it isn't implemented anymore, therefore
preventing running wasmer-wasi using wasmer itself.

Removing this buinding should do absolutely nothing, as it's not used
anywhere (anymore).

lib/wasi/src/lib.rs

@@ -113,12 +113,6 @@ impl From<WasiBusProcessId> for u32 {
     }
 }
 
-#[cfg(target_family = "wasm")]
-#[link(wasm_import_module = "__wbindgen_thread_xform__")]
-extern "C" {
-    fn __wbindgen_thread_id() -> u32;
-}
-
 #[derive(Debug, Clone)]
 pub struct WasiThread {
     /// ID of this thread