Fix Emergency Number API doc

1) remove documentation about null return
2) Map including the key*s* as the active subscription ID*s*

Bug: 130426238
Test: Treehugger
Change-Id: I4c9b682ef25378b9de91cd6255ed6fc514ea220d
Merged-In: I4c9b682ef25378b9de91cd6255ed6fc514ea220d
(cherry picked from commit aca6eb7dac0a307756d0c3e76b26503618f40df5)
1 file changed