Remove nesting of .dropdown-item, so it is less specific than
.gl-new-dropdown.

This could potentially change specificity in case of existing overrides.
For any `.dropdown-item`s that have another class applied that class
could now take precedence over the dropdown-menu styles. However every
instance I can find is adding utility classes, which are already
intentionally more specific than nested `.dropdown-item` (mostly utils
using `!important`)