In SERVER-48128 and its backport to 4.4.2, we introduced a function setIgnoredShardVersionForMergeCursors to set shard version IGNORED on $mergeCursors pipelines received by mongoD, so that MongoProcessInterface knows to version any internal commands run as part of the merging pipeline. This was because mongoS versions prior to 4.4.2 do not set any version on $mergeCursors pipelines before sending them to the shards. After we branch for 5.0, we can remove this code from master, since any mongoS capable of upgrading to 5.X will already be setting IGNORED on $mergeCursors.