augmented trees: apply config to speedup only tree fetches with aux

Summary:
apply config to speedup *only* tree fetches with aux metadata requested

There is a regression for fetching trees in Sapling, that are requested without
aux. To mitigate this, we should prefer the old code path for now for these
trees.

Meta:

the regression was identified by this scuba query: https://fburl.com/scuba/mononoke_test_perf/2u2ntf1e

Reviewed By: muirdm

Differential Revision: D63345271

fbshipit-source-id: b17375844f4021fb8ef6af4fbc328d7a306018a8

eden/scm/lib/edenapi/src/client.rs

@@ -503,7 +503,8 @@ impl Client {
             manifest_blob: attrs.manifest_blob,
             parents: attrs.parents,
             child_metadata: attrs.child_metadata,
-            augmented_trees: attrs.augmented_trees || self.config().augmented_trees,
+            augmented_trees: attrs.augmented_trees
+                || (self.config().augmented_trees && attrs.child_metadata),
         };
 
         let try_route_consistently = self.config().try_route_consistently;