Async closures will move params into the future always

compiler/rustc_error_codes/src/error_codes/E0708.md

@@ -1,12 +1,14 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 `async` non-`move` closures with parameters are currently not supported.
 
 Erroneous code example:
 
-```compile_fail,edition2018,E0708
+```edition2018
 #![feature(async_closure)]
 
 fn main() {
-    let add_one = async |num: u8| { // error!
+    let add_one = async |num: u8| {
         num + 1
     };
 }