mutation_partition: Replace value_comp with key_comp calls
mutation_partition: Replace value_comp with key_comp calls

This will reduce the size of bi::set API being used.

Signed-off-by: Piotr Jastrzebski <2c0eb4a25a7cde333ff2d0860cb06051925fd74f@scylladb.com>

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