Remove unused entry point

While investigating
https://gitlab.com/gitlab-org/gitlab/-/issues/233603, I discovered this
file which seems to be unused, so let's just remove it.

ee/app/assets/javascripts/protected_branches/index.js

-/* eslint-disable no-unused-vars */
-
-import $ from 'jquery';
-import ProtectedBranchCreate from '~/protected_branches/protected_branch_create';
-import ProtectedBranchEditList from './protected_branch_edit_list';
-
-$(() => {
-  const protectedBranchCreate = new ProtectedBranchCreate({ hasLicense: true });
-  const protectedBranchEditList = new ProtectedBranchEditList();
-});