Don't call $DONE twice in S25.4.4_A2.1_T3.js (#2679)

Reverts the change from 040eb5393a to avoid
calling $DONE twice in the test file.

test/built-ins/Promise/prototype/then/S25.4.4_A2.1_T3.js

@@ -37,6 +37,6 @@ Promise.resolve().then(function() {
     assert.sameValue(sequence.length, 3);
     checkSequence(sequence, "Expected 1,2,3");
   }).then($DONE, $DONE);
-}).then($DONE, $DONE);
+});
 
 sequence.push(1);