Fix spec violations in blob_content_viewer_spec.js

What does this MR do and why?

Removes setData() from blob_content_viewer_spec.js

Screenshots or screen recordings

No ui changes

Before	After

How to set up and validate locally

1. Checkout this branch git checkout -b 390977-fix-spec-violations-blob-content-viewer
2. run spec/frontend/repository/components/blob_content_viewer_spec.js in the console

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #390977 (closed)