Added remove subscription support

Bug: 239607619
Test: atest SubscriptionManagerServiceTest
      atest SubscriptionDatabaseManagerTest
Merged-In: Ia19ea13132420278b50ddb6c0faba29d9ddacbf2
Change-Id: Ia19ea13132420278b50ddb6c0faba29d9ddacbf2
5 files changed