To uninstall the BigFix Client, take action on Task ID: 219 TROUBLESHOOTING: Uninstall BES Client, and target the servers in question. The second action will completely remove all traces of the client.
Note: The BES Clients will not be able to report the final status of the action because they will be removed before the action completes. Instead, the BES Clients will stop responding and the action status will report back as ‘Evaluating’, ‘Failed’, or ‘Running’. You will need to manually remove the computer from the BES Console after the BES Client is uninstalled.
Removal of the Computers from BigFix can be accomplished as @menglish66 suggested, or you could wait for your computer removal scheduled tasks to clean things up.