Tidy up repo_tabs_spec

spec/javascripts/repo/repo_tabs_spec.js

@@ -9,16 +9,13 @@ describe('RepoTabs', () => {
   }, {
     id: 1,
   }];
+
   function createComponent() {
     const RepoTabs = Vue.extend(repoTabs);
 
     return new RepoTabs().$mount();
   }
 
-  beforeEach(() => {
-    spyOn(repoTabs.methods, 'isOverflow');
-  });
-
   it('renders a list of tabs', () => {
     RepoStore.openedFiles = openedFiles;
     RepoStore.tabsOverflow = true;