Remove unnecessary coupling between Promise tests and Object.observe

test/mjsunit/es6/debug-promises/reject-uncaught-all.js

Index: test/mjsunit/es6/debug-promises/reject-uncaught-all.js
diff --git a/test/mjsunit/es6/debug-promises/reject-uncaught-all.js b/test/mjsunit/es6/debug-promises/reject-uncaught-all.js
index beaf1878fef9943721a3659be876bd5e06bebad3..0b0c0c8e388e9675741dbf76e79dfdedad8ef8bd 100644
--- a/test/mjsunit/es6/debug-promises/reject-uncaught-all.js
+++ b/test/mjsunit/es6/debug-promises/reject-uncaught-all.js
@@ -60,10 +60,7 @@ function testDone(iteration) {
     }
   }
 
-  // Run testDone through the Object.observe processing loop.
-  var dummy = {};
-  Object.observe(dummy, checkResult);
-  dummy.dummy = dummy;
+  %EnqueueMicrotask(checkResult);
 }
 
 testDone(0);