Remove stack overflow handler stub for wasm.

Author: Vytautas Astrauskas

src/libstd/sys/wasm/stack_overflow.rs

@@ -1,11 +1,3 @@
-pub struct Handler;
-
-impl Handler {
-    pub unsafe fn new() -> Handler {
-        Handler
-    }
-}
-
 pub unsafe fn init() {}
 
 pub unsafe fn cleanup() {}