Replace usage on `dom` wrapper on element for native methods

1. appendChild
2. textContent
3. querySelector*
4. parentNode
5. removeChild
6. children

Leave all dom usage on Event untouched.

Change-Id: I01a3e9ae96dc65b296fbd1ae4f10cf1b132f90ee
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js
index a53304e..6ba9d36 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.js
@@ -30,7 +30,7 @@
 import '../gr-tooltip-content/gr-tooltip-content.js';
 import '../gr-confirm-delete-comment-dialog/gr-confirm-delete-comment-dialog.js';
 import '../gr-account-label/gr-account-label.js';
-import {flush, dom} from '@polymer/polymer/lib/legacy/polymer.dom.js';
+import {flush} from '@polymer/polymer/lib/legacy/polymer.dom.js';
 import {GestureEventListeners} from '@polymer/polymer/lib/mixins/gesture-event-listeners.js';
 import {LegacyElementMixin} from '@polymer/polymer/lib/legacy/legacy-element-mixin.js';
 import {PolymerElement} from '@polymer/polymer/polymer-element.js';
@@ -867,7 +867,7 @@
   }
 
   _openOverlay(overlay) {
-    dom(getRootElement()).appendChild(overlay);
+    getRootElement().appendChild(overlay);
     return overlay.open();
   }
 
@@ -877,7 +877,7 @@
   }
 
   _closeOverlay(overlay) {
-    dom(getRootElement()).removeChild(overlay);
+    getRootElement().removeChild(overlay);
     overlay.close();
   }