If you do not want to have the jobs, files and volumes from this client, from bconsole you can use "purge":
*purge
This command can be DANGEROUS!!!
It purges (deletes) all Files from a Job,
JobId, Client or Volume; or it purges (deletes)
all Jobs from a Client or Volume without regard
to retention periods. Normally you should use the
PRUNE command, which respects retention periods.
If you purge a volume, all the files and jobs associated to it are deleted from catalog.
To remove the client, you can delete the client resource definition from your bacula-dir.conf and then do a "reload" using bconsole. This will reload your new configurations without the deleted client.
Best regards,
Ana