Hide "Assignee" related components when disabled in config

This affects the dashboard column and the change metadata field.

Change-Id: Id2d46f5549b856da1c35892c3f547f58444e7eb6
diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.html b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.html
index 773e6ec..ce3770f 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata_test.html
@@ -634,6 +634,11 @@
       setup(() => {
         deleteStub = sandbox.stub(element.$.restAPI, 'deleteAssignee');
         setStub = sandbox.stub(element.$.restAPI, 'setAssignee');
+        element.serverConfig = {
+          change: {
+            enable_assignee: true,
+          },
+        };
       });
 
       test('changing change recomputes _assignee', () => {