Remove BaseField component

[youknowriad]

I've noticed that we have this component that is not used or exported anywhere. So it's not clear to me why we're keeping its code around. I believe it's probably a leftover from the G2 components migration to the Gutenberg repository. So I'm just removing it in this PR.

[github-actions]

Flaky tests detected in 0254072.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4132738390
📝 Reported issues:

• [Flaky Test] should display (capture the) text from the currently active link even if there is a rich text selection #36495 in specs/editor/various/links.test.js

[fabiankaegy]

I verified that this component isn't used anywhere by searching through the codebase. And since it isn't exported this removal looks good to me 👍

That being said I don't have much insight into how all of the G2 components were brought over.

[ciampo]

I can confirm, it looks like BaseField was part of the g2 suite of components. It looks like it's at the foundation of some other g2 components, like Select and TextField, which I believe never got introduced to this repository when the g2 migration slowed down.

It should be safe to remove it, thank you! We can always look at reintroducing it if/when working on an evolution of these components.