Explain tables have R/I , please check .../sqllib/misc/EXPLAIN.DDL for details. One way to cleanup is to drop and recreate them. You can also delete data or use load/replace from /dev/null to truncate them. Load can put them in checking pending state and you can use set integrity with the immediate unchecked option to take them out of checking pending without being checked for integrity violations.
We're on Z/OS, but same can be done on LUW. We unload(export) the most recent 3 versions then load replace to the tables. Pretty much same as our syspackage table, where we free anything prior to our most recent 3 versions.