Fix installer
Configuration from extension.json is not loaded by the installer. Hence
there is no 'ReadingLists' configuration yet. Use the main configuration
instead.
Stop passing MediaWikiServices::getInstance() to isCentralWiki()
The main configuration would still not have the extension setting
'ReadingListsCentralWiki', normalize it to false.
Bug: T196567
Change-Id: Icf707e60069070cebcda2906985d3960b3c555ec