Remove old migration spec.

From this point, the `services` table doesn't have the `build_events`
flag anymore. So instead of updating the spec for this, I removed
it. It should have been executed at this point.

spec/migrations/migrate_build_events_to_pipeline_events_spec.rb

-require 'spec_helper'
-require Rails.root.join('db', 'post_migrate', '20170301205640_migrate_build_events_to_pipeline_events.rb')
-
-# This migration uses multiple threads, and thus different transactions. This
-# means data created in this spec may not be visible to some threads. To work
-# around this we use the TRUNCATE cleaning strategy.
-describe MigrateBuildEventsToPipelineEvents, truncate: true do
-  let(:migration) { described_class.new }
-  let(:project_with_pipeline_service) { create(:empty_project) }
-  let(:project_with_build_service) { create(:empty_project) }
-
-  before do
-    ActiveRecord::Base.connection.execute <<-SQL
-      INSERT INTO services (properties, build_events, pipeline_events, type)
-      VALUES
-        ('{"notify_only_broken_builds":true}', true, false, 'SlackService')
-      , ('{"notify_only_broken_builds":true}', true, false, 'MattermostService')
-      , ('{"notify_only_broken_builds":true}', true, false, 'HipchatService')
-      ;
-    SQL
-
-    ActiveRecord::Base.connection.execute <<-SQL
-      INSERT INTO services
-        (properties, build_events, pipeline_events, type, project_id)
-      VALUES
-        ('{"notify_only_broken_builds":true}', true, false,
-         'BuildsEmailService', #{project_with_pipeline_service.id})
-      , ('{"notify_only_broken_pipelines":true}', false, true,
-         'PipelinesEmailService', #{project_with_pipeline_service.id})
-      , ('{"notify_only_broken_builds":true}', true, false,
-         'BuildsEmailService', #{project_with_build_service.id})
-      ;
-    SQL
-  end
-
-  describe '#up' do
-    before do
-      silence_migration = Module.new do
-        # rubocop:disable Rails/Delegate
-        def execute(query)
-          connection.execute(query)
-        end
-      end
-
-      migration.extend(silence_migration)
-      migration.up
-    end
-
-    it 'migrates chat service properly' do
-      [SlackService, MattermostService, HipchatService].each do |service|
-        expect(service.count).to eq(1)
-
-        verify_service_record(service.first)
-      end
-    end
-
-    it 'migrates pipelines email service only if it has none before' do
-      Project.find_each do |project|
-        pipeline_service_count =
-          project.services.where(type: 'PipelinesEmailService').count
-
-        expect(pipeline_service_count).to eq(1)
-
-        verify_service_record(project.pipelines_email_service)
-      end
-    end
-
-    def verify_service_record(service)
-      expect(service.notify_only_broken_pipelines).to be(true)
-      expect(service.build_events).to be(false)
-      expect(service.pipeline_events).to be(true)
-    end
-  end
-end