Allow pushBatchSize when cluster replication is enabled

Pushing in batches was disabled when replication.distributionInterval
is set because it produced more SEVERE "Error while deleting task" log
entries from ReplicationTasksStorage. Those errors are now logged at
FINE level when they are expected in a multi-primary setup, so there is
no longer a reason to ignore pushBatchSize in that case.

Change-Id: Iea59514cb3ee0c15290b095cc2460bb3062b0ee2