Remove the task_list test since it is patched upstream

spec/lib/banzai/filter/task_list_filter_spec.rb

-require 'spec_helper'
-
-describe Banzai::Filter::TaskListFilter, lib: true do
-  include FilterSpecHelper
-
-  it 'does not apply `task-list` class to non-task lists' do
-    exp = act = %(<ul><li>Item</li></ul>)
-    expect(filter(act).to_html).to eq exp
-  end
-
-  it 'applies `task-list` to single-item task lists' do
-    act = filter('<ul><li>[ ] Task 1</li></ul>')
-
-    expect(act.to_html).to start_with '<ul class="task-list">'
-  end
-end