Remove check whether window.Polymer is defined

This check was done to protect GWT UI page from loading PG plugin. Given
that GWT UI is removed, this check is now obsolete and can be removed.

Change-Id: If8e9eb6fccd889de11e886903c893f5f47d02830
diff --git a/plugin.html b/plugin.html
index 138397d..7118174 100644
--- a/plugin.html
+++ b/plugin.html
@@ -18,11 +18,9 @@
 
 <dom-module id="delete-repo">
   <script>
-    if (window.Polymer) {
-      Gerrit.install(function(plugin) {
-          plugin.registerCustomComponent(
-              'repo-command', 'gr-delete-repo');
-      });
-    }
+    Gerrit.install(function(plugin) {
+        plugin.registerCustomComponent(
+            'repo-command', 'gr-delete-repo');
+    });
   </script>
 </dom-module>