The mergeScheduler, mergePolicy and luceneAutoCommit no-longer-supported warnings date back to 2012. Let's remove them from 7.0.0 onwards for clarity. This caught my attention as part of SOLR-8668's mergePolicy support removal.
Remove support for <mergePolicy> (in favour of <mergePolicyFactory>)
Deprecate/Remove <indexDefaults> and <mainIndex> in favor of <indexConfig> in solrconfig.xml