incremental_reader_selector: Remove unecessary check for duplicated next_token
incremental_reader_selector: Remove unecessary check for duplicated next_token

The next_token will never be the same as the current _selector_position,
unless they are both maximum_token, which is already handled.

Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Message-Id: <9c54ae07a18d201185027c9b533bcb5256bead8a.1505826102.git.a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

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