Clean up E0423 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0423.md

@@ -1,8 +1,7 @@
 An identifier was used like a function name or a value was expected and the
 identifier exists but it belongs to a different namespace.
 
-For (an erroneous) example, here a `struct` variant name were used as a
-function:
+Erroneous code example:
 
 ```compile_fail,E0423
 struct Foo { a: bool };