If you have no use for data in the cel database table, you should consider changing the Asterisk configuration to disable CEL events. That can be done by "enable=no" in the cel.conf (or an included configuration file).
To delete the CEL events from the database table and reclaim the space used by the database table, you should
1. Login into mysql as root or a user that has rights to modify the database (e.g., if the database name is asteriskcdrdb, you would use "mysql -p -u root asteriskcdrdb")
2. Delete all rows in the cel table ("DELETE FROM cel;")
3. Optimize the database table to reclaim the space ("OPTIMIZE TABLE cel;")