Remove RunBackupReceiver

Currently, the logic for backupnow is split between UserBackupManagerService,
RunBackupReceiver and BackupHandler. This makes it very confusing as
the pre checks are split over three classes and there's no obvious
reason why it is like that.

On the other hand, requestBackup is split nicely into checks in
UserBackupManagerService and starting the work from BackupHandler.

This change removes RunBackupReceiver for backupNow and splits the logic
only between UserBackupManager and BackupHandler - in the direction of
making it consistent with requestBackup by moving the checks to
UseBackupManagerService. (except the check for isBackupRunning which
needs to be in the same synchronised block as setBackupRunning).

Also, this CL moves the wakelock acquire from RunBackupReceiver (removed in this CL)
to BackupHandler. Previously, RunBackupReceiver would acquire the wakelock and then
send MSG_RUN_BACKUP. BackupHandler would then have to release that wakelock when it finds
it cant run the backup because there's no transport.
Now, the acquire is in BackupHandler after checking the transport. Therefore we dont need
that release (when there's no transport) anymore

A side benefit is we get rid of an extra hop to the broadcast receiver
so potentially backups should be scheduled (albeit very slightly)
faster.

Test: atest -v RunBackupFrameworksServicesRoboTests
Test: atest -v $(find frameworks/base/services/tests/servicestests/src/com/android/server/backup -name '\''*Test.java'\'')
Test: atest -v CtsBackupTestCases
Test: atest -v CtsBackupHostTestCases

Bug: 147741497
Change-Id: I40051540c7e8531ef05076eab7ccc5b44b0c08d2