Update error message and un-xfail test

Author: catamorphism

src/test/compile-fail/issue-2123.rs

@@ -1,6 +1,4 @@
-// xfail-test
-// error-pattern:unresolved import: m::f
-use x = m::f;
+use x = m::f; //~ ERROR failed to resolve import
 
 mod m {
     #[legacy_exports];