usb: gadget: fusb300_udc: drop dead code

that code has been dead forever. Since the
first commit (0fe6f1d1

) the use of that code
has been commented out. Let's drop the dead
code already and fix the following compile
warning:

| drivers/usb/gadget/fusb300_udc.c: At top level:
| drivers/usb/gadget/fusb300_udc.c:771:13: warning: ‘fusb300_wrfifo’ defined but not used [-Wunused-function]
| drivers/usb/gadget/fusb300_udc.c:1027:13: warning: ‘fusb300_set_ep_bycnt’ defined but not used [-Wunused-function]

Signed-off-by: Felipe Balbi <balbi@ti.com>