[Lens] Fixes bug with removing layer with trendline

[stratoula]

Summary

Part of #143687

If you create a layer with trendline and try to clear the layer, there was an error. This PR fixes it.

[elasticmachine]

Pinging @elastic/kibana-vis-editors @elastic/kibana-vis-editors-external (Team:VisEditors)

[dej611]

Tested locally with Safari 👍

[drewdaemon]

This fix makes sense to me! I think @MichaelMarcialis also wanted the "clear layer" icon not to change to the "delete layer" trash can. We could do this by excluding hidden layers when we calculate isOnlyLayer.

https://github.com/elastic/kibana/blob/main/x-pack/plugins/lens/public/editor_frame_service/editor_frame/config_panel/config_panel.tsx#L275

[MichaelMarcialis]

I think @MichaelMarcialis also wanted the "clear layer" icon not to change to the "delete layer" trash can.

Yes, exactly. Since the metric type visualizations only support a single layer, the button should retain its "Clear layer" action (with accompanying eraser icon).

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 9257e77

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
lens	1.3MB	1.3MB	+171.0B

History

• 💛 Build #81695 was flaky 9cb51db

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[drewdaemon]

I spoke with @stratoula and we'll get that icon change ironed out in another PR @MichaelMarcialis .

Thank you for taking on this fix @stratoula !