Replace `dht/sharder.hh` with a "smaller" header, which provides
just the enough dependencies.
in f744007e, we traded `database.hh` with a smaller set of headers.
but it turns out `dht/sharder.hh` can be replaced with a even smaller
one. because `dht::sharder` is defined by `dht/token-sharding.hh`, and
what we need from `dht/sharder.hh` is this class's declaration.
`clang-include-cleaner` identified this issue.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#21881
03599477af