Clear calling identity n BackupManager#reportDelayedRestoreResult

The method binds BackupTransport, which needs to happen from system
process.

Bug: 280047012
Test: 1. Modify TelephonyBackupAgent to call
         BackupManager#reportDelayedRestoreResult
      2. Observe there's no exception.
Change-Id: I84ee31fa7d08f1f4714e303c33e64ed61503c452