Apply deliver-most-recent policy to LOGIN_ACCOUNTS_CHANGED.

This will allow us to discard older LOGIN_ACCOUNTS_CHANGED
broadcasts that are still waiting to be delivered when a new
LOGIN_ACCOUNTS_CHANGED broadcast is sent.

Bug: 271030977
Test: atest services/tests/servicestests/src/com/android/server/accounts/AccountManagerServiceTest.java
Change-Id: I46d6179c934ac9541f591f3ac9af742bb7b91eaf