Remove .autocomplete-results inset border that is occluded by items

[neildaniels]

Individual . autocomplete-item children of .autocomplete-results all have a background color, which completely covers the inset border.

This becomes evident if any individual items have margin overrides, or the parent results view has additional padding added.

/cc @primer/ds-core

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[simurai]

@neildaniels thanks for noticing. 🙇

I can't really remember, but I think initially the intention was to show a border, but not for the .autocomplete-item when they are selected (blue background):

But that regressed later when we added a white background to support using <button> or <a> elements for .autocomplete-item.

Hmm.. maybe we should just add a normal border instead. Selected items will not go edge to edge, but maybe the safer option and matches the .suggester.

I'll commit and push straight to this branch.

[simurai]

Ok, this looks ready to ship... 🚢 👍