Fix unnecessary horizontal scroll area in pipeline visualizations

What does this MR do?

Removes a min-width attribute for the build pipeline visualization wrapper

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

I am curious why this line was there in the first place. Perhaps I'm just not seeing it.

Why was this MR needed?

I was noticing an unnecessary horizontal scroll bar when viewing pipeline visualizations embedded in merge request builds tab: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5627/builds

What are the relevant issue numbers?

Line appears to have been introduced in !5742 (merged)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

As this is a very simple cosmetic change, I don't think it warrants inclusion in the changelog, documentation, or tests.

• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together