Remove unused code from gr-dropdown

This was a remnant of an earlier refactoring and was caught by an error
in fried-twinkie.

Change-Id: I3bea46250a9d901c4e6ef3ea25bfe5ad27e634a1

polygerrit-ui/app/elements/shared/gr-dropdown/gr-dropdown.js

@@ -62,8 +62,6 @@
         value() { return []; },
       },
 
-      _hasAvatars: String,
-
       /**
        * The elements of the list.
        */
@@ -85,12 +83,6 @@
       'up': '_handleUp',
     },
 
-    attached() {
-      this.$.restAPI.getConfig().then(cfg => {
-        this._hasAvatars = !!(cfg && cfg.plugin && cfg.plugin.has_avatars);
-      });
-    },
-
     _handleUp(e) {
       if (this.$.dropdown.opened) {
         e.preventDefault();