Update gitlab-dangerfiles to 2.6

Dangerfile

@@ -2,10 +2,4 @@
 
 require 'gitlab-dangerfiles'
 
-gitlab_dangerfiles = Gitlab::Dangerfiles::Engine.new(self)
-gitlab_dangerfiles.import_plugins
-gitlab_dangerfiles.import_dangerfiles
-
-danger.import_plugin('danger/plugins/*.rb')
-
-danger.import_dangerfile(path: File.join('danger', 'roulette'))
+Gitlab::Dangerfiles.for_project(self, 'labkit-ruby', &:import_defaults)

danger/plugins/project_helper.rb

-# frozen_string_literal: true
-
-module Danger
-  # Common helper functions for danger scripts
-  class ProjectHelper < ::Danger::Plugin
-    def changes
-      # We do not need to categorize files in this code base
-      helper.changes([])
-    end
-
-    def project_name
-      "labkit-ruby"
-    end
-  end
-end

danger/roulette/Dangerfile

-# frozen_string_literal: true
-
-MESSAGE = <<MARKDOWN
-## Reviewer roulette
-
-Changes that require review have been detected! A merge request is normally
-reviewed by both a reviewer and a maintainer in its primary category and by a
-maintainer in all other categories.
-MARKDOWN
-
-TABLE_MARKDOWN = <<MARKDOWN
-
-To spread load more evenly across eligible reviewers, Danger has picked a candidate for each
-review slot. Feel free to
-[override these selections](https://about.gitlab.com/handbook/engineering/projects/#labkit-ruby)
-if you think someone else would be better-suited
-or request help in the `#labkit` Slack channel.
-
-To read more on how to use the reviewer roulette, please take a look at the
-[Engineering workflow](https://about.gitlab.com/handbook/engineering/workflow/#basics)
-and [code review guidelines](https://docs.gitlab.com/ee/development/code_review.html).
-
-Once you've decided who will review this merge request, mention them as you
-normally would! Danger does not automatically notify them for you.
-
-| Reviewer | Maintainer |
-| -------- | ---------- |
-MARKDOWN
-
-def note_for_spins_role(spins, role)
-  spins.each do |spin|
-    note = note_for_spin_role(spin, role)
-
-    return note if note
-  end
-
-  'No %{role} available' % { role: role }
-end
-
-def note_for_spin_role(spin, role)
-  spin.public_send(role)&.markdown_name(author: roulette.team_mr_author) # rubocop:disable GitlabSecurity/PublicSend
-end
-
-def markdown_row_for_spins(spins_array)
-  reviewer_note = note_for_spins_role(spins_array, :reviewer)
-  maintainer_note = note_for_spins_role(spins_array, :maintainer)
-
-  "#{reviewer_note} | #{maintainer_note} |"
-end
-
-if project_helper.changes.any?
-  project = project_helper.project_name
-
-  random_roulette_spins = roulette.spin(project, [nil], timezone_experiment: false)
-
-  rows = random_roulette_spins.map do |spin|
-    markdown_row_for_spins([spin])
-  end
-
-  markdown(MESSAGE)
-  markdown(TABLE_MARKDOWN + rows.join("\n")) unless rows.empty?
-end