XWIKI-9779
Partial revert of 71ebf97d which ate the line tabbing in XWiki.Registration
Revert "XWIKI-9516: Create a new Wiki API that replaces xwiki-platform-wiki-manager and xwiki-platform-workspace."

This reverts commit 71ebf97d9b228926bfcb088f47888fca802acb46.

Conflicts:
	xwiki-platform-core/xwiki-platform-wiki/xwiki-platform-wiki-ui/xwiki-platform-wiki-ui-wiki/src/main/resources/XWiki/Registration.xml
XWIKI-9779: XWiki.Registration executes $doAfterRegistration twice
Once is because of the null check which unintentionally executes the code, thanks Anca for debugging it.