Fix delete action not filling dropdown in labels management

What does this MR do and why?

Fixes a bug where the "Delete" action was not filling the width in the actions dropdown, as other dropdown items do. This also removes the rounded border from both delete and promote actions.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open the <Project|Group> Information > Labels page (http://gdk.test:3000/flightjs/Flight/-/labels) from a project or group where you can manage labels
2. Click the ellipsis button to open the actions menu on a label
3. Focus/hover the Delete item to see that it's the correct width

MR acceptance checklist

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