KeyValueStore:: do_transactions: clean up code which is never used
clean up ops and bytes which is never used in do_transactions()

Signed-off-by: Ning Yao <zay11022@gmail.com>
Merge pull request #3278 from mslovy/wip-y04

KeyValueStore:: do_transactions: clean up code which is never used

Reviewed-by: Haomai Wang <haomaiwang@gmail.com>