Remove red line under the header

This was used to indicate whether you were using shadow dom under
polymer 1.x. This is no longer needed as we are going to Polymer 2.x.

Change-Id: Icdb3224a1226f05514076d9a1fcb93e77be42772
diff --git a/polygerrit-ui/app/elements/gr-app-element.html b/polygerrit-ui/app/elements/gr-app-element.html
index af4d799..20f5996 100644
--- a/polygerrit-ui/app/elements/gr-app-element.html
+++ b/polygerrit-ui/app/elements/gr-app-element.html
@@ -72,10 +72,6 @@
         padding: 0 var(--default-horizontal-margin);
         border-bottom: 1px solid var(--border-color);
       }
-      gr-main-header.shadow {
-        /* Make it obvious for shadow dom testing */
-        border-bottom: 1px solid pink;
-      }
       footer {
         background-color: var(--footer-background-color);
         border-top: 1px solid var(--border-color);
@@ -125,7 +121,6 @@
       <gr-main-header
           id="mainHeader"
           search-query="{{params.query}}"
-          class$="[[_computeShadowClass(_isShadowDom)]]"
           on-mobile-search="_mobileSearchToggle">
       </gr-main-header>
     </gr-fixed-panel>
@@ -191,7 +186,7 @@
         <div class="errorMoreInfo">[[_lastError.moreInfo]]</div>
       </div>
     </main>
-    <footer r="contentinfo" class$="[[_computeShadowClass(_isShadowDom)]]">
+    <footer r="contentinfo">
       <div>
         Powered by <a href="https://www.gerritcodereview.com/" rel="noopener"
         target="_blank">Gerrit Code Review</a>
diff --git a/polygerrit-ui/app/elements/gr-app-element.js b/polygerrit-ui/app/elements/gr-app-element.js
index 3f41e5b..af69af8 100644
--- a/polygerrit-ui/app/elements/gr-app-element.js
+++ b/polygerrit-ui/app/elements/gr-app-element.js
@@ -73,7 +73,6 @@
       _lastError: Object,
       _lastSearchPage: String,
       _path: String,
-      _isShadowDom: Boolean,
       _pluginScreenName: {
         type: String,
         computed: '_computePluginScreenName(params)',
@@ -123,7 +122,6 @@
 
     ready() {
       this.$.reporting.appStarted(document.visibilityState === 'hidden');
-      this._isShadowDom = Polymer.Settings.useShadow;
       this.$.router.start();
 
       this.$.restAPI.getAccount().then(account => {
@@ -403,10 +401,6 @@
       this.$.registrationOverlay.close();
     },
 
-    _computeShadowClass(isShadowDom) {
-      return isShadowDom ? 'shadow' : '';
-    },
-
     _goToOpenedChanges() {
       Gerrit.Nav.navigateToStatusSearch('open');
     },