Set x-frame-option to sameorigin to allow the Sidekiq iframe to display.
Revert "Set x-frame-option to sameorigin to allow the Sidekiq iframe to display."

This reverts commit 754b0838e0c2857b0ca73d2ced675ed5b3042242.

Sidekiq rendered via mounted sinatra app. We don't need to change
controller headers. It won't affect sidekiq at all. Please modify nginx
config instead for all gitlab app.
Ensure sidekiq is displayed by setting X-Frame-Options.
Merge branch 'same-origin-header' into 'master'

Same origin header

Fixes #1313