Remove default icon from PluginBlockSettingsMenuItem

[HardeepAsrani]

Description

Remove default icon from PluginBlockSettingMenuItem as the new Gutenberg UI
doesn't have icons by default. Closes #21390

How has this been tested?

Tested with a plugin that uses PluginBlockSettingMenuItem with and without passing the icon.

Types of changes

Enhancement: If someone uses PluginBlockSettingMenuItem without an icon, their menu item will stop displaying the default Plugin icon.

Checklist:

• [ x ] My code is tested.
• [ x ] My code follows the WordPress code style.
• [ x ] My code follows the accessibility standards.
• [ x ] My code has proper inline documentation.
• [ x ] I've included developer documentation if appropriate.
• [ x ] I've updated all React Native files affected by any refactorings/renamings in this PR.

[karmatosed]

From a design perspective, this feels fine for me as I can see a default could be an unexpected experience. I am going to loop in @jasmussen here though to get an opinion on how this impacts the toolbar as it might mean complications there.

[jasmussen]

I would agree, this seems like a good change. We should be intentional about using icons in menus. Nice work.

[gziolo]

Let's get it in, thank you 👍