targets/fomu: modification to ValentyUSB no longer required.

Following commits make it generic/portable while still using IOBuffers:
litex-hub/valentyusb@77b9d01
litex-hub/valentyusb@371526e

litex_boards/targets/fomu.py

@@ -83,7 +83,6 @@ def __init__(self, bios_flash_offset, sys_clk_freq=int(12e6), **kwargs):
 
         # Serial -----------------------------------------------------------------------------------
         # FIXME: do proper install of ValentyUSB.
-        # FIXME: replace IoBuf with https://github.com/im-tomu/valentyusb/blob/master/valentyusb/usbcore/io.py#L13-L61.
         os.system("git clone https://github.com/litex-hub/valentyusb -b hw_cdc_eptri")
         sys.path.append("valentyusb")