reconcilable_result_builder: remove v1 support
reconcilable_result_builder: remove v1 support

Amounts to making the range tombstone consume() overload private. It is
still used internally to consume the downgraded (from v2) range
tombstones.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla