Revert of Disable non-standard Promise functions in staging

test/mjsunit/es6/promises.js

Index: test/mjsunit/es6/promises.js
diff --git a/test/mjsunit/es6/promises.js b/test/mjsunit/es6/promises.js
index d02f7b7ef3e869e3ffede7bba2a9f3308044a601..478f216eb1ca2bea6f38634e3be3385870f0b5fc 100644
--- a/test/mjsunit/es6/promises.js
+++ b/test/mjsunit/es6/promises.js
@@ -25,7 +25,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Flags: --allow-natives-syntax --harmony-tostring --promise-extra
+// Flags: --allow-natives-syntax --harmony-tostring
 
 // Make sure we don't rely on functions patchable by monkeys.
 var call = Function.prototype.call.call.bind(Function.prototype.call)