The implementation file contained some documentation. This has been moved
to the Haiku Book (and is rewritten in most cases). The documentation gives
some insight on how the notification_server works.
Change-Id: I82bafcf57101d4882bdf07e7f731df9cd8adc861
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2299
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>