[Lens] Rename "reset layer" in single layer visualizations

[flash1293]

Right now there's a "reset layer" button for each layer:

However, this button is also shown for non-layer-based visualizations like table or pie:

This seems like a weird way of phrasing the button because the layer concept doesn't really apply in this case.

In this case it should get renamed to "Reset visualization"

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[mbondyra]

@flash1293, just to make this clear:

1. For pie, datatable, metric or any other allowing only one layer visualization, we should display reset visualization
2. For xy chart (visualization allowing more than one layer) when only one layer exists, we should display reset layer
3. For xy chart (visualization allowing more than one layer) when more than one layer exist, we should display delete layer

Is this correct?

[flash1293]

@mbondyra Yes, exactly

[anish-khanna]

If nobody has tried to clean up this issue, I'd like to do so!

[flash1293]

@anish-khanna Sure, thanks for participating! I'll assign the issue to you, let me know if you can't work on it anymore.