ArgsTable: Remove the "simple" detection for enum types

[phated]

Issue: Partial reversion of #11868

What I did

While working on a very large storybook, I noticed that a subset of types weren't formatted correctly. For example, they had no background. They were really standing out from the rest of the system. These types often looked like (arg1: string) => 'return1' | 'return2'.

I traced it back to the simple option added in #11868 which added a check that is too simplistic for what it is trying to do. From what I understand, it was trying to avoid adding styling to complex unions, but it didn't consider a union-type value anywhere else in a signature.

My suggestion is to remove this check for now until a more sophisticated check is applied.

How to test

• Is this testable with Jest or Chromatic screenshots? The previous PR said it added these?
• Does this need a new example in the kitchen sink apps? No
• Does this need an update to the documentation? No

If your answer is yes to any of these, please make sure to include it in your PR.

[phated]

cc @ajkl2533 as well.

[shilman]

WFM cc @ajkl2533