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/sidebar/sidebar.js

@@ -9,10 +9,6 @@ const viewTitles = {
 };
 
 BlazeComponent.extendComponent({
-  template() {
-    return 'sidebar';
-  },
-
   mixins() {
     return [Mixins.InfiniteScrolling, Mixins.PerfectScrollbar];
   },
@@ -232,10 +228,6 @@ Template.membersWidget.onRendered(draggableMembersLabelsWidgets);
 Template.labelsWidget.onRendered(draggableMembersLabelsWidgets);
 
 BlazeComponent.extendComponent({
-  template() {
-    return 'addMemberPopup';
-  },
-
   onCreated() {
     this.error = new ReactiveVar('');
     this.loading = new ReactiveVar(false);

client/components/sidebar/sidebarArchives.js

@@ -1,8 +1,4 @@
 BlazeComponent.extendComponent({
-  template() {
-    return 'archivesSidebar';
-  },
-
   tabs() {
     return [
       { name: TAPi18n.__('cards'), slug: 'cards' },

client/components/sidebar/sidebarFilters.js

@@ -1,8 +1,4 @@
 BlazeComponent.extendComponent({
-  template() {
-    return 'filterSidebar';
-  },
-
   events() {
     return [{
       'click .js-toggle-label-filter'(evt) {
@@ -37,10 +33,6 @@ function mutateSelectedCards(mutationName, ...args) {
 }
 
 BlazeComponent.extendComponent({
-  template() {
-    return 'multiselectionSidebar';
-  },
-
   mapSelection(kind, _id) {
     return Cards.find(MultiSelection.getMongoSelector()).map((card) => {
       const methodName = kind === 'label' ? 'hasLabel' : 'isAssigned';