Get rid of priority setting for USB sharing notifications.

Default priority is fine - the notification persists for 8 seconds and
won't wake the display.

Fixed: 1117307
Change-Id: I2734a1391b7679224e2fb24e319dc4320aace59b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2389283
Commit-Queue: Nicholas Verne <nverne@chromium.org>
Commit-Queue: David Munro <davidmunro@google.com>
Auto-Submit: Nicholas Verne <nverne@chromium.org>
Reviewed-by: David Munro <davidmunro@google.com>
Cr-Commit-Position: refs/heads/master@{#803743}

chrome/browser/chromeos/usb/cros_usb_detector.cc

@@ -240,7 +240,6 @@ void ShowNotificationForDevice(device::mojom::UsbDeviceInfoPtr device_info) {
       rich_notification_data,
       base::MakeRefCounted<CrosUsbNotificationDelegate>(
           notification_id, std::move(device_info)));
-  notification.SetSystemPriority();
   SystemNotificationHelper::GetInstance()->Display(notification);
 }