Optimizing usage of `currentColor` in CSS

[webmandesign]

Issue description
currentColor is a default value for various CSS properties. So, there is no need to set it up as border-color in certain cases, for example.

Expected behavior
Not using currentColor value when redundant.

Additional context

• Gutenberg v4.5.1

[webmandesign]

I've removed currentColor from borders recently.

Still, there is a questionable usage of the value in /packages/editor/src/components/inserter-list-item/style.scss file. There are 2 instances of currentColor that could be replaced with inherit in my opinion. Surely, the result would be the same, so this is for reconsideration.