Remove some unused code

[crazytonyli]

Description

WordPressKit.BloggingPromptsServiceRemote.fetchPrompts is not used, which is deleted in the first commit.

All the rest is deleting Bloganuary related code, which is not likely to come back (see p5uIfZ-gxX-p2).

[dangermattic]

	1 Warning
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

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[wpmobilebot]

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

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	32297
	Version	PR #25577
	Bundle ID	com.jetpack.alpha
	Commit	bd26aca
	Installation URL	4g0r2tvtufd5g

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[wpmobilebot]

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

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	32297
	Version	PR #25577
	Bundle ID	org.wordpress.alpha
	Commit	bd26aca
	Installation URL	66iib9t4k4g90

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