Remove opaque type obligation and just register opaque types as they are encountered.

This also registers obligations for the hidden type immediately.

compiler/rustc_lint/src/builtin.rs

@@ -1675,7 +1675,6 @@ impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
                     Coerce(..) |
                     ConstEvaluatable(..) |
                     ConstEquate(..) |
-                    OpaqueType(..) |
                     TypeWellFormedFromEnv(..) => continue,
                 };
                 if predicate.is_global() {