Fix

FileObserver memory leak, If an application use FileObserver funtion startWatching some files, then stopWatching, WeakReference will leak in mRealObservers container.

Bug: 379797597
(cherry picked from https://android-review.googlesource.com/q/commit:c004cd180c8fb8aa60bd512877915f4a72c49569)
Merged-In: Ibbcae08c1d38f7b8a8e295368e251c3b074d461c
Change-Id: Ibbcae08c1d38f7b8a8e295368e251c3b074d461c
Flag: EXEMPT bug fix