Unify multiple sequential_promise_test definitions.

LayoutTests/bluetooth/bluetooth-helpers.js

 var genericAccessServiceUuid = '00001800-0000-1000-8000-00805f9b34fb';
 var genericAttributeServiceUuid = '00001801-0000-1000-8000-00805f9b34fb';
 var glucoseServiceUuid = '00001808-0000-1000-8000-00805f9b34fb';
 var heartRateServiceUuid = '0000180d-0000-1000-8000-00805f9b34fb';
 var batteryServiceUuid = '0000180f-0000-1000-8000-00805f9b34fb';
-
-var promise_tests = Promise.resolve();
-// Helper function to run promise tests one after the other.
-// TODO(ortuno): Remove once https://github.com/w3c/testharness.js/pull/115/files
-// gets through.
-function sequential_promise_test(func, name) {
-  var test = async_test(name);
-  promise_tests = promise_tests.then(function() {
-    return test.step(func, test, test);
-  }).then(function() {
-    test.done();
-  }).catch(test.step_func(function(value) {
-    // step_func catches the error again so the error doesn't propagate.
-    throw value;
-  }));
-}