Remove obsolete MySQL sync caching code and fix connection reuse issue
Remove obsolete MySQL sync caching code and fix connection reuse issue

zebulon2/dataserver,zebulon2/dataserver,grumbelbart/zotero_dataserver_sualk,zebulon2/dataserver,zebulon2/dataserver,grumbelbart/zotero_dataserver_sualk,grumbelbart/zotero_dataserver_sualk,grumbelbart/zotero_dataserver_sualk