mutation_partition: Make row_tombstones_entry ReversiblyMergeable
mutation_partition: Make row_tombstones_entry ReversiblyMergeable

raphaelsc/scylla,duarten/scylla,scylladb/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,raphaelsc/scylla,scylladb/scylla,kjniemi/scylla,raphaelsc/scylla,duarten/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla