cql3/statements/select_statement: Don't double count unpaged queries
cql3/statements/select_statement: Don't double count unpaged queries

Unpaged queries are those for which the client didn't enable paging,
and we already account for them in
indexed_table_select_statement::do_execute().

Remove the second increment in read_posting_list().

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>
Message-Id: <20181003121811.11750-1-a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

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