remove unneeded `before_action`

app/controllers/projects/pipelines_controller.rb

 class Projects::PipelinesController < Projects::ApplicationController
   before_action :whitelist_query_limiting, only: [:create, :retry]
   before_action :pipeline, except: [:index, :new, :create, :charts]
-  before_action :commit, only: [:show, :builds, :failures]
   before_action :authorize_read_pipeline!
   before_action :authorize_create_pipeline!, only: [:new, :create]
   before_action :authorize_update_pipeline!, only: [:retry, :cancel]
@@ -168,10 +167,6 @@ class Projects::PipelinesController < Projects::ApplicationController
                     .present(current_user: current_user)
   end
 
-  def commit
-    @commit ||= @pipeline.commit
-  end
-
   def whitelist_query_limiting
     # Also see https://gitlab.com/gitlab-org/gitlab-ce/issues/42343
     Gitlab::QueryLimiting.whitelist('https://gitlab.com/gitlab-org/gitlab-ce/issues/42339')