Reword description in zremrangebyscore spec

"Should" is unnecessary in spec descriptions as it is implied.

Change-Id: I1e77bb758635a3107ebada7deb86c4d75ac5786d
Reviewed-on: http://gerrit.causes.com/37709
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>