Remove unnecessary template name declaration

This code was duplicate with the name we use to `register` the
component. A update of blaze-component removed the need to duplicate
this declaration.

client/components/activities/activities.js

@@ -1,10 +1,6 @@
 const activitiesPerPage = 20;
 
 BlazeComponent.extendComponent({
-  template() {
-    return 'activities';
-  },
-
   onCreated() {
     // XXX Should we use ReactiveNumber?
     this.page = new ReactiveVar(1);