[NAN] Remove OnNanDown notification from API

Duplicates the WIFI_NAN_STATE_CHANGED_ACTION broadcast. Remove
all state information from manager.

Bug: 28622807
Change-Id: I00632b216edb2dd74412861c4b46f01adec5a271
(cherry picked from commit cbf37593325f48168aa1aa49b12d30fe43345cc1)
3 files changed