[Android Notification Channels] Remove TODO

- I no longer think this TODO to remove the DCHECK is necessary:
 It's appropriate to DCHECK since we should only ever create a channel
if the old status is UNAVAILABLE, or the same as the new status (to
handle the possibility that two code paths try to create a channel at
the same time, e.g. during channel migration).

Bug: 700377
Change-Id: I0554d2962051863a6c38a9f9ccb262f905f6a241
Reviewed-on: https://chromium-review.googlesource.com/544842
Commit-Queue: Anita Woodruff <awdf@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517834}

chrome/browser/notifications/notification_channels_provider_android.cc

@@ -388,8 +388,6 @@ void NotificationChannelsProviderAndroid::CreateChannelIfRequired(
   } else {
     auto old_channel_status =
         bridge_->GetChannelStatus(channel_entry->second.id);
-    // TODO(awdf): Maybe remove this DCHECK - channel status could change any
-    // time so this may be vulnerable to a race condition.
     DCHECK_EQ(old_channel_status, new_channel_status);
   }
 }