Update error code description

Author: jonas-schievink

compiler/rustc_error_codes/src/error_codes/E0744.md

@@ -2,25 +2,15 @@ An unsupported expression was used inside a const context.
 
 Erroneous code example:
 
-```compile_fail,E0744
+```compile_fail,edition2018,E0744
 const _: i32 = {
-    let mut x = 0;
-
-    for i in 0..4 { // error!
-        x += i;
-    }
+    async { 0 }.await
 };
 ```
 
-At the moment, `for` loops, `.await`, and the `Try` operator (`?`) are forbidden
-inside a `const`, `static`, or `const fn`.
+At the moment, `.await` is forbidden inside a `const`, `static`, or `const fn`.
 
 This may be allowed at some point in the future, but the implementation is not
-yet complete. See the tracking issues for [`async`] and [`?`] in `const fn`, and
-(to support `for` loops in `const fn`) the tracking issues for [`impl const
-Trait for Ty`] and [`&mut T`] in `const fn`.
+yet complete. See the tracking issue for [`async`] in `const fn`.
 
 [`async`]: https://github.com/rust-lang/rust/issues/69431
-[`?`]: https://github.com/rust-lang/rust/issues/74935
-[`impl const Trait for Ty`]: https://github.com/rust-lang/rust/issues/67792
-[`&mut T`]: https://github.com/rust-lang/rust/issues/57349