Adding a per-uid cap on concurrent alarms

Reasonably, it is seen that most apps have a low number of alarms inside
alarm manager at any given time. In rare cases, app bugs can lead to
spam resulting in memory and computation pressure on the system.

(Also, removing some unused code)

Test: atest FrameworksMockingServicesTests:AlarmManagerServiceTest
atest CtsAlarmManagerTestCases

Bug: 31832077
Change-Id: Ie537e644619a787b7a730dc567aafa0258ae57f0