Remove lightbox and stickyfill

[toitzi]

Description

Removing Plugins Lightbox and stickyfill, as those are outdated and not used by koseven.ga website

Type of change

• [x] Bug fix
• [ ] New feature

Checklist

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.