Update uitest stderrs

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

compiler/rustc_error_codes/src/error_codes/E0466.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 Macro import declaration was malformed.
 
 Erroneous code examples:
 
-```compile_fail,E0466
+```compile_fail
 #[macro_use(a_macro(another_macro))] // error: invalid import declaration
 extern crate core as some_crate;