Do not send X-WMF-UUID header if the user has opted out of EventLogging.

If the user has opted out of EventLogging then we shouldn't be tracking them
at all. This includes unique counting using the app install ID. This patch
ensures that the app install ID not transmitted if the user has opted out.

Bug: T85243
Change-Id: Ie6b9aea9708d382119372febd9b8c849360fd5ef