Refactored some UserManager.getUsers(excludeDying) calls.

Replaced by getUsers() when exlcudeDying was hardcoded to false, or
getUsers(true,  excludeDying, true) when it was a variable.

This refactoring will help replacing getUsers(true) to getAliveUsers().

Bug: 157921703

Test: m
Test: atest atest LockscreenFrpTest LockSettingsServiceTests SyntheticPasswordTests

Change-Id: I139462ab329fe46d8136eae0a39ac071a7e019db