RFR: 8273071: SeparatorSkin: must remove child on dispose

[Ambarish Rapte]

On Thu, 2 Sep 2021 12:45:02 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

> minor skin cleanup issue: SeparatorSkin didn't remove the line it added to the control's children
> 
> fix is to override dispose and include the removal
> for testing: removed the exclusion of SeparatorSkin from memoryLeakTest - doing so lets it fail/pass before/after this fix

looks good to me.

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Marked as reviewed by arapte (Reviewer).

PR: https://git.openjdk.java.net/jfx/pull/616