Disable other sorting when using the new relevance computation

This actually makes the scores slightly worse, but I think it's important
that we understand the quality of the scores without other sorting. The
scores are still better than with the old computation.

Change-Id: I514aa35029b600b9ab87bf531064f1e89b02774a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/139682
Reviewed-by: Jaime Wren <jwren@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart

@@ -212,7 +212,7 @@ class DartCompletionManager implements CompletionContributor {
                 stackTrace));
         await contributionSorter.sort(dartRequest, suggestions);
       }
-    } else {
+    } else if (!request.useNewRelevance) {
       await contributionSorter.sort(dartRequest, suggestions);
     }
     performance.logElapseTime(SORT_TAG);