Remove unused page size in pipeline list query

This change removes the `.per(30)` that gets overridden
by the page size when the list of pipelines is shown.

app/controllers/projects/pipelines_controller.rb

@@ -39,7 +39,7 @@ class Projects::PipelinesController < Projects::ApplicationController
       .new(project, current_user, index_params)
       .execute
       .page(params[:page])
-      .per(30)
+      .per(20)
 
     @pipelines_count = limited_pipelines_count(project)