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What you can do is: get a list of all desktop pools with full clones first:
VMware Horizon Server API - VMware API Explorer - VMware {code}
with a filter on source = virtual_center and type is automated
From those desktop pools you can get the machines using :
VMware Horizon Server API - VMware API Explorer - VMware {code}
with a filter on the pools
and with the machine id's you can delete them using:
VMware Horizon Server API - VMware API Explorer - VMware {code}