You can disable (remove) it in vm-properties (show all devices), and later add if you need it. I removed floppy from all my VMs, it is no good for anything today...
These forum @notification thingies work!
EFI doesn't provide a way to disable the floppy drive controller itself. With recent virtual hardware versions, the firmware should automatically track and handle the addition/removal of virtual floppy drives – There is no longer any need to ensure that the firmware is aware of the number of virtual floppies and to enable/disable them individually, as there is with BIOS – but the FDC will always be enabled by firmware, as far as I can tell.
If you're using a Windows guest, you can go into Device Manager, right-click on the Standard floppy disk controller device and choose Disable. The net effect will be the same as if the firmware was configured to disable the floppy controller... it just won't take effect until the OS has launched.
Let us know if that meets your needs!