repair: Make repair_meta::to_repair_rows_list a static function
repair: Make repair_meta::to_repair_rows_list a static function

It allows pulling out the logic of convering on-the-wire representation
of repair mutations to an internal representation used later for
flushing repair mutations to disk. This in turn is needed to unit test
the functionality without spinning up clusters, which significantly
improves developer iteration time.

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