Remove shard version checks from cursor_valid_after_shard_stepdown

cursor_valid_after_shard_stepdown.js checks for shard version UNKNOWN after the step up of a secondary. If a refresh happens on the secondary from a mirrored read or other source, this assertion will fail.

This ticket is to remove the shard versioning checks from this test and re-enable it in the sharding_max_mirroring suite