storage_proxy: paxos_response_handler::prune: fixup indentation
storage_proxy: paxos_response_handler::prune: fixup indentation

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20200405115046.733450-2-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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