Remove leftover UserDirectoryLivetableResultsOverride from WikiManager

This file here https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-wiki/xwiki-platform-wiki-ui/xwiki-platform-wiki-ui-wiki/src/main/resources/WikiManager/UserDirectoryLivetableResultsOverride.xml seems to not be used anymore, there is an override in the XWiki space in the same application, here https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-wiki/xwiki-platform-wiki-ui/xwiki-platform-wiki-ui-wiki/src/main/resources/XWiki/UserDirectoryLivetableResultsOverride.xml . The 2 pages look "the same" as in having had the same code at some point. They should at least be refactored in a single file if they're still both needed, to avoid code duplication.