Hide filters UI in Roadmap within epic page

What does this MR do and why?

This MR is a follow-up on !71398 (merged) where Roadmap filters UI would show momentarily (i.e. while data is being loaded) within an epic page. So this MR does a couple of things;

• Fix the ~bug where Roadmap filtering UI shows up on Epic page.
• Clean up tests for Roadmap component.

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