When your host uses a network adapter with iBFT, the software iSCSI adapter is always enabled by default.
After your ESXi host's first boot, the software iSCSI adapter is enabled and appears in the vSphere Web Client on the list of storage adapters.
The iBFT-enabled network adapter on your host causes the software iSCSI to be always present. This condition occurs even when you do not use iBFT for the iSCSI boot.
If you do not use the iBFT-enabled network adapter for the iSCSI boot and do not want the software iSCSI adapter to be enabled, remove the iBFT configuration from the network adapter. Because this process is vendor-specific, consult your vendor documentation for details.