Components: Cleanup Dashicons component

[gziolo]

Description

This is a follow-up for #17356 where we refactored IconButton component to no longer pass down ariaPressed prop. This means that it's no longer used in the code and it should be removed from the child components which were reading its value.

I checked the history and it looks like ariaPressed was introduced in #11827. It was never really used in the web code. Should it be also removed in other places?

In particular, I think about Dashicon implementation which used to pass this prop down but it seems to longer be necessary. See:

gutenberg/packages/components/src/dashicon/index.js

Line 895 in eb3a82f

const iconClass = getIconClassName( icon, className, ariaPressed );

I updated Dashicon to look closer to:
https://github.com/WordPress/dashicons/blob/master/react/index.jsx

Testing

Steps from #17356 are the best way to validate it:

• Run the example app with Xcode 11 beta
• Check that the toolbar colors are correct on the toolbar (following the screenshots)
• Check that the rest of the icons in the app shows properly
• In particular the BottomSheet icons (Add link / Image settings)
• Check that the icon Subscript is colored properly (Numbers on H1, H2, etc...)

[etoledom]

Tested: Icons on blocks, toolbars, block appender and bottom sheets.
On iOS Dark and Light mode, and Android.

Everything seems to work perfectly 🎉

Thank you @gziolo !