Remove background_jobs-specific headers.

app/controllers/admin/background_jobs_controller.rb

 class Admin::BackgroundJobsController < Admin::ApplicationController
   def show
-    use_secure_headers_override(:background_jobs)
-
     ps_output, _ = Gitlab::Popen.popen(%W(ps -U #{Gitlab.config.gitlab.user} -o pid,pcpu,pmem,stat,start,command))
     @sidekiq_processes = ps_output.split("\n").grep(/sidekiq/)
   end

config/initializers/secure_headers.rb

@@ -50,8 +50,3 @@ SecureHeaders::Configuration.default do |config|
     config.csp[:script_src] << "maxcdn.bootstrapcdn.com"
   end
 end
-
-SecureHeaders::Configuration.override(:background_jobs) do |config|
-  config.csp[:frame_ancestors] = %w('self')
-  config.x_frame_options = 'SAMEORIGIN'
-end