before this change, we always reference the return value of
`make_reader()`, and the return value's type `flat_mutation_reader_v2`
is movable, so we can just pass it by moving away from it.
in this change, instead of using a lambda, let's just have the
return value of it. simpler this way.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#16835
09a688d325