Remove old BackupManagerService

As discussed, only removed the class, local interface and trampoline
still exist. That will go into a next CL.

Bug: 65823538
Test: make RunFrameworksServicesRoboTests
Test: runtest -p com.android.server.backup frameworks-services
Test: gts-tradefed run commandAndExit gts-dev -m GtsBackupTestCases
Test: gts-tradefed run commandAndExit gts-dev -m GtsBackupHostTestCases
Test: cts-tradefed run commandAndExit cts-dev -m CtsBackupTestCases
Test: adb shell bmgr backupnow <kv and full-backup packages>
Test: adb backup & adb restore
Change-Id: Ifcb4c02e364b8c4899ff376ff20cd8c89fc1af28