Remove some errors in UI tests

As we now need to run THIR unsafeck before MIR build, errors in unsafeck can cause the compilation to be aborted earlier.

src/test/ui/async-await/async-unsafe-fn-call-in-safe.rs

@@ -16,6 +16,6 @@ async fn g() {
 }
 
 fn main() {
-    S::f(); //~ ERROR call to unsafe function is unsafe
-    f(); //~ ERROR call to unsafe function is unsafe
+    S::f(); //[mir]~ ERROR call to unsafe function is unsafe
+    f(); //[mir]~ ERROR call to unsafe function is unsafe
 }