Remove stage/unstage buttons from IDE commit list items

What does this MR do?

Removes the stage, unstage & discard buttons from the list items in the IDE commit panel. These actions are possible through either the buttons above the file editor.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51695

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides