Remove extra spaces from MR discussion notes

What does this MR do?

Removes extra spaces from MR discussion notes.

Are there points in the code the reviewer needs to double check?

notes_line selectors are totally eliminated.

Why was this MR needed?

While there have been large spaces on the left side of the MR discussion note forms, we can use those spaces more efficiently.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • [n/a] Has been reviewed by Backend
  • [n/a] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [n/a] Internationalization required/considered
• [n/a] End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #46340 (closed)