Un-XFAIL vector-no-ann

and update it to reflect the new friendly error message

Author: catamorphism

src/test/compile-fail/vector-no-ann.rs

@@ -1,10 +1,6 @@
 // xfail-stage0
-// xfail-stage1
-// xfail-stage2
-// xfail-stage3
 
-// error-pattern:3:13:3:14
+// error-pattern:Ambiguous type
 fn main() -> () {
   auto foo = [];
 }
-// this checks that span_err gets used