Remove polymorphization

compiler/rustc_codegen_cranelift/example/polymorphize_coroutine.rs

@@ -1,17 +0,0 @@
-#![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
-
-use std::ops::Coroutine;
-use std::pin::Pin;
-
-fn main() {
-    run_coroutine::<i32>();
-}
-
-fn run_coroutine<T>() {
-    let mut coroutine = #[coroutine]
-    || {
-        yield;
-        return;
-    };
-    Pin::new(&mut coroutine).resume(());
-}