OpDml::Delete in snapshots

The following discussion from !478 (merged) should be addressed:

• @rosik started a discussion:

  This logic misses a case when a tuple was deleted. Instead, it should truncate the space and insert everything from the snapshot. But I suggest to move this concern into a separate issue and fix it later.

See also:

• a13a3031 (test/conftest.py:511)
• a13a3031 (test/int/test_snapshot.py:37)