DOCS-14733 shard routing for aggregations (#340) (#352)

Co-authored-by: jason-price-mongodb <[email protected]>

Co-authored-by: jason-price-mongodb <[email protected]>

Author: jason-price-mongodb

source/core/aggregation-pipeline-sharded-collections.txt

@@ -20,14 +20,10 @@ sharded collections.
 Behavior
 --------
 
-.. versionchanged:: 3.2
-
-If the pipeline starts with an exact :pipeline:`$match` on a shard key,
-the entire pipeline runs on the matching shard only. Previously, the
-pipeline would have been split, and the work of merging it would have
-to be done on the primary shard.
-
-.. versionchanged:: 3.6
+If the pipeline starts with an exact :pipeline:`$match` on a
+:term:`shard key`, and the pipeline does not contain :pipeline:`$out` or
+:pipeline:`$lookup` stages, the entire pipeline runs on the matching
+shard only.
 
 When aggregation operations run on multiple shards, the results are 
 routed to the :binary:`~bin.mongos` to be merged, except in the
@@ -53,4 +49,3 @@ To see how the pipeline was split, include the :method:`explain
 :method:`db.collection.aggregate()` method.
 
 .. include:: /includes/fact-optimizations-subject-to-change.rst
-