Remove unused field after flag cleanup

int mNotificationClientUid was used when this class could handle one notification at a time. With the implementation of handling simultaneous alarms it has become unused.

Also adding @SuppressLint annotation to a private method to stop the warning.

Bug: 432469009
Test: manual
Flag: EXEMPT removing unused code
Change-Id: I88c89510c81b25ca62d305238e964dacd52b70fb