intent: drop unused headers
intent: drop unused headers

neither of these headers is used in this header file. and neither
is `bi` namespace alias used.

so in this change, the unused headers and unused namespace alias
are removed.

Signed-off-by: Kefu Chai <cdc92d111bae0ed1ee3b3c8a1f849fcffc6b44f7@gmail.com>

syuu1228/seastar,scylladb/seastar,scylladb/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar