Remove empty RunnerProject spec

spec/models/runner_project_spec.rb

-# == Schema Information
-#
-# Table name: runner_projects
-#
-#  id         :integer          not null, primary key
-#  runner_id  :integer          not null
-#  project_id :integer          not null
-#  created_at :datetime
-#  updated_at :datetime
-#
-
-require 'spec_helper'
-
-describe RunnerProject do
-  pending "add some examples to (or delete) #{__FILE__}"
-end