Remove RAMDirectoryFactory after RAMDirectory removal?

This is a spinoff from LUCENE-8474. RAMDirectory is now officially gone from Lucene, replaced by a different memory-backed (byte buffers) implementation. Should we rename RAMDirectoryFactory in Solr or just change the implementation, leaving the name as is and looking at it as an implementation detail?

RAMDirectoryFactory is used in a lot of places, so it a compatibility-breaking change (that doesn't add any value). I'm keen on leaving it as is, but looking for feedback from those more familiar with Solr deployments.