[App size reduction] Remove `domain-credit` asset and related code

[iamgabrielma]

Description

This PR removes the usage of the unused domain-credit image as part of reducing the app size on WOOMOB-534. After checking with Kiwi folks it seems we no longer have an entry point for the domain purchase feature as a whole ( https://github.com/woocommerce/woocommerce-ios/pull/15680 ), so I took the opportunity to clean up the related code as well.

I've only removed the code directly coupled with the feature, happy to remove the rest in this same PR (there's still files remaining under the /domains folder as well as 2 test suites that we might not need to run anymore).

Testing information

• CI should pass
• From my understanding of this feature, we should still see no Domains row under Menu tab > Settings, on a WPCom test store without a custom domain, and no other entry points or access to the deleted files since the DomainSettingsCoordinator is out of the settings controller, but let me know if I missed something.

[dangermattic]

	1 Warning
:warning:	This PR is larger than 300 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

Generated by :no_entry_sign: Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	30510
	Version	PR #15754
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	cd47709eb3b20026a9cb28afb4bd9340dd2376c1
	Installation URL	26f4jfbfk9es0

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[itsmeichigo]

Hi @iamgabrielma - could you please remove all the domain folder and tests? I don't think keeping them around is useful.

[iamgabrielma]

Hi @iamgabrielma - could you please remove all the domain folder and tests? I don't think keeping them around is useful.

No problem! I've removed the domain folder and tests from the woo layer, but there's still dead code in Yosemite and Networking. This can be handled separately, as this PR is already close to 3k lines 👍