More cleanup of tracking core.

A sequel to !1887 (merged)

• Cleaned up ca::TrackFinderWindow.
• Cleaned up ca::TripletConstructor.
• Removed fCurrentIterationIndex and access to it from ca::WindowData.

requested review from @s.zharko

assigned to @se.gorbunov

merged

mentioned in merge request !1902 (merged)

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added CodeOwners label

added Tracking label