Remove unused class in mini pipeline graph

What does this MR do?

This MR removes a class that is no longer used in the mini pipeline graph at the MR widget:

Initially it was used when to reposition the icons when the pipeline had an extra downstream icon, but has since then been phased out, this is the place:

Related to #300403 (closed) as a first step to clean up these components.

Screenshots (strongly suggested)

No changes:

before	after

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

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #300403 (closed)