PEGA keeps all external jars in a DB table called pr_engineclasses, mapped to System-Runtime-Code class. You can delete the relevant rows from the table, and do a server restart. That should fix the issue.
Also, please take a DB backup whenever you install a new external JAR. That is the correct way to do it.
In order to filter effectively you can use the codeset version you have used while importing the jar. Server start is must to take effect. Also, going forward, you can place the jar at external location in order to avaoid such things.