SOLR-4718 support was added for reading solr.xml from ZK by providing system property solr.solrxml.location=zookeeper. If this property is not specified, solr.xml is read from SOLR_HOME. This issue is a spinoff from SOLR-7727 where start scripts do not support solr.xml in ZK.
Instead of adding this to start scripts, suggest to simplify the whole logic:
- If not in cloud mode, require solr.xml in SOLR_HOME as today
- If in cloud mode, first look for solr.xml in ZK, but if not found, load from SOLR_HOME as today
- Remove the need for solr.solrxml.location property