Ignore snapshot isolation conflict during fragment removal, before
streaming transaction commits. This happens when a streaming
transaction creates a read view that precedes the INSERTion of
fragments into the streaming_log table. Fragments are INSERTed
using a different transaction. These fragment are then removed
as part of COMMIT of the streaming transaction. This fragment
removal operation could fail when the fragments were not part
the transaction's read view, thus violating snapshot isolation.
