drive: Fix a bug that broke "Delta Update Status" in chrome:drive-internals

$('polling-interval-sec') no longer exists hence causes a JS error.
FWIW, the regression was introduced in crrev.com/194294

BUG=233446
TEST=open chrome:drive-internals; confirm that Delta Update Status section is shown properly.

Review URL: https://codereview.chromium.org/14366011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195062 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/chromeos/drive_internals.js

@@ -189,8 +189,6 @@ function updateLocalMetadata(localMetadata) {
 function updateDeltaUpdateStatus(deltaUpdateStatus) {
   $('push-notification-enabled').textContent =
         deltaUpdateStatus['push-notification-enabled'];
-  $('polling-interval-sec').textContent =
-        deltaUpdateStatus['polling-interval-sec'];
   $('last-update-check-time').textContent =
         deltaUpdateStatus['last-update-check-time'];
   $('last-update-check-error').textContent =