Make "SD Card removed" notification dismissible if the removed SD Card is not the primary storage

The Galaxy S uses the "external SD Card" as the extended storage
and it the notification should be dismissible as it's okay not
to have it.

Additionally, this patch also not hide the USB storage mount dialog
if the removed storage is not the primary storage

Adapted for JB 4.2

Change-Id: Ic752a3da917e0d7736a619fb68f07905106987fb

Conflicts:
	packages/SystemUI/src/com/android/systemui/usb/StorageNotification.java