[Part 3] Clean up :apollo_boards feature flag

What does this MR do and why?

Remove mentions of :apollo feature flag for remaining tests and the following components (all remaining ones):

• BoardNewEpic
• BoardSettingsWipLimit
• EpicLane
• EpicSwimlanes
• IssuesLaneList
• ToggleEpicsSwimlanes

Steps	MR
Part 1	!137614 (merged)
Part 2	!138006 (merged)
Swimlanes and leftovers	You are here
Delete VueX store	TBD

Screenshots or screen recordings

No visual changes

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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 #430042 (closed)