Remove `stage_button.vue` and `unstage_button.vue` files

What does this MR do?

Remove dead code in stage_button and unstage_button and the files where these components are used. Issue - #118785 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content