RFR: 8374208: Remove superfluous field in XYChart

[John Hendrikx]

On Tue, 23 Dec 2025 20:01:22 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> This change removes an unnecessary field `XYChart.Data.series` as it is mirrored by the `seriesProperty`, something I failed to see twice - first during code review [0] I did not realize a property was added that mirrors the field, then I wrongly thought it was added in [1].
> 
> Now is the time to gather stones.
> 
> [0] https://git.openjdk.org/jfx/pull/1016
> 
> [1] https://git.openjdk.org/jfx/pull/2013

Marked as reviewed by jhendrikx (Reviewer).

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PR Review: https://git.openjdk.org/jfx/pull/2018#pullrequestreview-3610790007